Every aquarium at one time or another experiences a bloom of brown algae. You are most likely to see it during the cycling phase of a new tank or while curing Live Rock. Brown algae can also show up at any time in well established tanks.

Brown algae is not an algae at all, but a tiny animal called a diatom. The animal is encased in a hard shell made out of silicone dioxide. The brown mats and film you see are composed of billions of diatoms interlocked together by their hard shells. They come in a variety of shapes and sizes and is the most common phytoplankton on the planet.

The appearance of brown algae in an aquarium is most often blamed on silicates in the tank water. Just like SPS corals that require calcium to grow, diatoms require silicates to grow. However, there are many other factors that cause brown algae and I believe the excess silicates story is way overplayed.

The use of “play sand” or silica gravel in a marine aquarium is often cited as a cause of diatoms. The silicates in these substances are bound up chemically much the same way as it is in glass. In fact, the glass panes that make up your aquarium is pretty much 100% silicates. The notion that play sand is a cause of diatoms is nothing more than another “reef legend”.

Almost every newly set up tank, during its cycling period, experiences a brown algae bloom. Even tanks with nothing but water and a layer of aragonite gravel will get it. Then if by magic, the brown algae begins to recede all by itself and is replaced by green algae.

During cycling, there is a time when the water contains high levels of dissolved organic carbons (DOCs) and nitrites, but low levels of nitrates and phosphates. It is these condition where diatoms seem to thrive. Minimizing their growth can be accomplished by turning the lights off during cycling. These are photosynthetic creatures and will not do well in subdued lighting. Secondly, performing large water changes and/or aggressive skimming during cycling will reduce their growth.

In established tanks, brown algae blooms are often times accompanied by some Cyanobacteria (red slime) as well. This is clearly an indication that it is an organics issue. Generous use of carbon and wet skimming will solve this problem.

When a brown algae bloom does occur, it is important to remove as much of it as possible. Similar to red slime, brown algae tends to “feed itself” through a die off and growth cycle that becomes self-sustaining.

Too much iodine in the water leads to brown algae. Even if you don’t use Lugol’s solution, check the label on any additives you use. Many contain significant amounts of iodine.

On rare occasions, excess silicates can be the cause. If you suspect this, phosphate removers also remove silicates. If you run phosphate removers all the time, it is highly unlikely that silicates are to blame. Still, silicates can get into your tank in a variety of ways. Using tap water or well water for topoff or salt mixing is a major source. Frozen Foods are another, though probably not a significant source.

Very high nitrate levels, even when phosphate and organics levels low will cause brown algae. No one knows the mechanism of this. Safe to say that It is prudent to keep nitrate levels low not only to prevent brown algae, but to prevent health problems with specimens in the tank.

Tanks with a good growth of green algae never seem to have brown algae problems. Perhaps the greens compete for nutrients, or more likely green algae consumes unknown compounds required for diatom growth. Whatever the cause, if one was to choose the lesser of two evils, green algae would be my choice.

In the mid 1970’s, Peter Wilken published a book entitled The Saltwater Aquarium for Tropical Marine Invertebrates. This landmark publication was one of the first to introduce a more natural approach to keeping sensitive invertebrates in aquaria. As time moved on, the “Invertebrate Aquaria” was renamed the “Reef Aquarium”, and the filtering techniques described by Mr. Wilkens later became known as the Berlin Method.

The Berlin Method is simple. It includes only three items to do all aquarium filtration: Live Rock, an overflow with mechanical filter, and a large Protein Skimmer.

Each of these items work together to complete the filtration picture. The Live Rock performs the function of a biological filter and provides nitrate reduction. The mechanical filter removes detritus and algae that naturally accumulates due to the metabolism of the invertebrates. And the protein skimmer removes nitrates, phosphates, and DOCs (dissolved organic carbons).

It’s been over thirty years since the original publication, and no one has come up with a better way to filter a reef tank. Sure, we now have Sulfur Filters, Phosphate Reactors, and a slew of other equipment at our disposal. But all this extra junk just boosts the power of the original Berlin design.

Somewhere along the way, many hobbyists decided that the mechanical filter in the Berlin Method was not necessary. Some go as far as stating it’s downright detrimental in keeping corals. The reason you most often hear is that mechanical filters remove pods and zooplankton that otherwise would feed the corals in the tank.

Quite frankly, this is bullshit. And here’s why.

No one can grow or sustain zooplankton in a reef aquarium. Period. Zooplankton is an “organism soup” of micro life that lives in the water column, most of which remain in a planktonic state and “free float” for their entire lives. Reef aquariums cannot produce the immense quantities of phytoplankton and other micron-size live food particles to sustain any populations of zooplankton. On the real reef, zooplankton is abundant and is consumed every night by corals and fish larvae. Unfortunately, these microorganisms simply don’t exist and never will in your aquarium. So a mechanical filter cannot remove zooplankton, because there isn’t any to remove.

Secondly, there are the Pods. Copepods, Amphipods, and Isopods can easily reproduce in large numbers in a reef aquarium. But the pods that grow well in our tanks are all benthic, meaning that they are bottom-dwelling creatures that don’t live in the water column. Have you ever experienced your front glass being covered by little white moving dots? These are Isopods. But you may have also noticed that the water didn’t look like it was snowing with them- only surfaces like the front glass and the Live Rock were populated. The don’t swim- they walk. The only way these little guys will feed your corals is if they accidentally crawl into a polyp. A mechanical filter will not remove Isopods unless they lose their footing and get swept into your overflow.

The larger Amphipods are quite common and can be seen crawling around on the Live Rock. As far as pods go, these guys are pretty big at around 5000 microns (about an 1/8-inch) as adults. The have a hard shell with a series of legs underneath and resemble a very tiny shrimp. They are an excellent food for Mandarins and other bottom feeding fish. They are however, too large to feed SPS polyps and too small to feed LPS corals. They guys would have to walk into the mouths of LPS corals to get eaten, which is not going to happen. These pods live everywhere- both in the sump/refugium and in the main tank. Unfortunately, most are too big to survive the trip through the return pump back to the main tank. Again, a mechanical filter might trap a few that get swept away by the current, but not enough to make a difference.

I decided to examine the contents of a used mechanical filter under a microscope. The filter sock I examined was in service for 3 weeks on a 60 gallon SPS reef tank. It’s pore size is 100 microns and composed of spun polypropylene. All of water flowing from the main tank through the overflow passed 100% through this filter. Within the 3 week time period, it was so clogged up that water would not freely pass through it anymore.

I took several scrapings of the material on the inside of the bag and placed it on well slides. The first thing I saw were diatoms (aka brown algae). Zillions and zillions of them. In the photo above, you can see the brown color of the spent filter sock caused by all the diatoms. Surprisingly, there is very little brown algae spots or brown haze anywhere on the glass panels in the aquarium.

Probably 90% of the material on the filter sock was brown algae. But there were also green microalgae and small strands of what appeared to be hair algae in great abundance. As for life forms, there were some very tiny (2-4 micron) single celled organisms swimming around. I don’t believe the 100 micron filter sock had captured these guys. They were just swimming in the droplets of water on both side of the filter material.

Finally, lots of detritus chunks. Many were entangled in a stringy algae mess, some pieces were clearly encased in a bacterial slime. Others looked like small rocks. At least this time, I did not find even one pod in the half-dozen or so scrapings I examined.

So what does this all mean?

While the Berlin Method touts the mechanical filter as a detritus removal mechanism, my own experimentation indicates that it’s main function is that of an algae filter. Both substances are equally harmful to the health of saltwater aquariums. Detritus robs the tank of oxygen and lowers PH and ORP. Algae smothers out invertebrates and causes severe water problems. While many things contribute to algae outbreaks, my opinion is that using a mechanical filter will diminish the occurrence of film algae, and prevent the spread of undesirable macro and hair algae. Besides, once you start using a mechanical filter, you will have the cleanest sump in town.

If you don’t already employ a mechanical filter in your reef tank, give it a try. I believe it is an important component of both algae and water quality control.

Marine Fish Compatibility

I don’t know how many times I’ve seen those fish compatibility charts. I’m sure you’ve seen plenty of them, too. They consist of rows and columns illustrating what species of marine fish can be safely kept together. Some of them go a step further and rate the compatibility as “Safe”, “Generally Safe”, ”Some Caution”, and so on. In my opinion, these charts are practically worthless.

Here’s why. You would never want to keep a Clown Trigger (Balistoides conspicillum) with a Pajama Cardinal (Sphaeramia nematoptera). But you could keep one or more Cardinals with a Niger Trigger (Odonus niger). Likewise, a Sailfin Tang (Zebrasoma veliferum) would get along with any Butterflyfish, but only if the tang is smaller in size. If you’re adding a fish to your tank that hasn’t had a new fish added in 8 months or more, I don’t care what kind of fish you have in there, the existing fish will be aggressive to the new addition- and some fish will remain that way, including the “peaceful” fish from the chart. For these reasons you cannot solely rely on fish compatibility charts in creating your community aquarium.

So where can you go to get all this information? I would recommend that the Internet be your last resort. There is just too much mis-information there. Start with your LFS, who has to deal with separating incoming shipments every week

and knows a lot about fish compatibility. Seek out veteran aquarists who have kept the species you’re interested in and can give you some first hand knowledge. Do invest in a few good books (such as Marine Fishes by Scott Michaels) to learn about compatibility issues and interaction.

When you have gotten to the point where you have selected a list of fish and have researched compatibility to the point where you believe they should all get along, consider the following:

► On a new tank setup, add the most peaceful and/or the smallest fish first. Work your way up from there. The largest and most aggressive fish should be added last. Unless you have multiple quarantine tanks, you will be adding a new fish (or groups of the same fish) at one month intervals. This is a good schedule to be on. It give the fish time to settle in and allows the tank to stabilize and adjust to the new bioload. Any problems along the way (like algae blooms) can be dealt with quickly. While the fish is in quarantine, it will learn to eat the food that you plan on feeding the community tank.

► The method of adding a new fish to an established aquarium depends on the situation. If the new fish is larger than all the rest, you can usually get away with adding the new fish and have some short term aggression. If the fish is small or you have gone a long time without adding any fish to the community tank, place the fish in a plastic specimen box drilled with holes and secure it to the rim of the aquarium. This give the established residents time to recognize the fish and ease away from their strong territorial instincts. Keep the fish in the specimen box for at least 3 days. Some authors advocate an alternative of rearranging the décor and live rock and add the fish directly. This method has not worked for me. It seems that some fish know that they are in the same tank and quickly reestablish territories. Others get so stressed out that their health suffers.

► Some fish do best in groups. For example, Damselfishes and Chromis. You should always keep these fish together through quarantine and when adding them to the display tank. Doing so will not only minimize stress but reduce aggression of existing fish when added as a group.

► During the first 24 hours, the new addition may hide most of the time and skip the first feeding. If it skips the second feeding, it may never acclimate to your tank.

► If the new addition is always in hiding and you never see it, it may have perished from either stress or aggression or both. This may sound crazy, but if the established fishes “gang up” and kill the new addition, you will never be able to add another fish to the tank again.

► If the new fish is harassed to the point where it is cowering in a corner, remove the fish immediately (or its aggressor). I have seen this happen on several occasions and can say that this level of stress will kill the fish in 24-48 hours, even if there is no fin damage.

► “Chasing” for the first 24 hours is normal for a new addition, but fin nipping is not. If there is significant fin damage even though the fish is swimming around and not huddled in a corner, you need to remove the fish as soon as possible. Place it back into quarantine until its fins are healed, and use the specimen box method to re-introduce it.

► For larger tanks, you probably feed your fish in the same area every day, perhaps on the left, right, or middle of the tank. Don’t confuse your fish by adding a new addition in the same location where you feed.

► If you cycle your lights down at night (perhaps turning off daylight bulbs before actinics), add the new fish when the lights are at their lowest level. But don’t add a new fish in total darkness. Some people advocate adding the fish during feeding or immediately thereafter. Personally, I’ve tried this and it doesn’t seem to make any difference. After all, territorial aggression is based on establishing a breeding nest and has nothing to do with food.

► Don’t add a new fish and go off to work. You want to stick around and check on it from time to time to make sure the acclimation is going well. Watch from a distance. Rapid movement right in front of the tank just adds to every fishes stress level.

► Once the new fish is settled in you might see some occasional chasing, which is harmless. This will subside over time.

There is no doubt that the biggest selling maintenance product in the aquarium industry is Activated Carbon. This long time filter media started as Bone Charcoal 150 years ago, and it’s been keeping aquarium water sparkling clear ever since.

In the aquarium trade, activated carbon is sold in more products than you think. It is the key ingredient in HOB disposable filter cartridges, and is often blended with ion exchange resins, ammonia removers, and other chemical media that makes up hundreds of aquarium products . And of course, it is sold in bulk or pure form for use in canister filters, mesh bags, and media reactors.

Why do we keep using it? Any veteran freshwater or marine aquarist can tell you that it removes odors, removes color, and makes aquarium water as clear as ice. Despite the beauty of your show tank, no one likes to walk into your living room and get a whiff of that “fishy” smell.

There is a lot of confusion about how activated carbon acts in saltwater, especially when it is used in reef aquariums. Here, aquarists are constantly pushing for a more natural filtration approach. But it bugs the hell out of me when I read all the misinformation on the Internet and even on carbon product labels. They preach to use carbon sparingly, like one day or three days a month, or don’t use it all. Folks, Activated Carbon is non-toxic. It cannot be overdosed. It will not remove all the salts and trace elements and turn your tank into some incomplete blend of synthetic seawater.

We all need to realize that our reef and fish-only aquariums are NOT miniature slices of the ocean. They may look that way, but bio-chemically they are an ecosystem that is always on the verge of collapse. Activated Carbon’s job is to remove metabolic wastes, or more commonly called organics. You can employ the deepest sand bed or the largest calcium reactor or a humongous circulation pump, but none of these things will have any effect on organics.

When it comes to organics, the world’s oceans maintain a perfect balance of metabolic waste removal through a series of natural recycling systems. Both the volume of water and the immense surface area provides a home for tens of thousands of species of macro and micro organisms that process these wastes. In the home aquarium, just a small fraction of these organisms can survive. Coupled with an extremely high specimen to water ratio, organics tend to accumulate in closed systems, and can reach concentrations orders of magnitude beyond natural ocean levels. Even with aggressive water changes, these organics can never be diluted enough to mimic the natural levels where our livestock has lived for thousands of years.

Don’t confuse organics with ammonia, nitrites, or nitrates. The bacteria responsible for breaking down these nutrients naturally thrive in all aquariums. Most tanks are nutrient rich and provide lots of food for these bacteria to thrive. Organics on the other hand, consists of complex metabolic compounds including phenols, organic acids, proteins, fats, carbohydrates, and hormones. To break these down, we don’t (and can’t) grow the right bacteria in our aquariums. In fact, detritus on the gravel surface and in the bottom of the sump are organic compounds that have reached such high concentrations that they fall out of solution. These particles remain inert as long as pH, oxygen, and ORP levels stay constant. Any wild swings or disruptions will trigger detritus particles to release these pollutants back into solution, causing an avalanche effect which will fuel a tank crash like there’s no tomorrow.

Where Do Organics Come From?

Creation of organics is a natural process of fish and invertebrate metabolism. It has little to do with the amount of food added to the tank. Reef tanks are especially vulnerable to organics, since corals and invertebrates produce a lot more organics than fish. Coral “slime” is nearly 100% pure organics. When you are mounting a coral or moving things around, copious amounts of sliming results. This slime is torn apart by powerheads, oozes through mechanical filters, and finally winds up being dissolved in the aquarium water. By contrast, coral slime in the ocean is quickly washed away perhaps hundreds of meters away from the coral. It is then consumed whole by other invertebrates or fish or quickly broken down by specialized bacteria and used by plankton as food. Everything is recycled in the ocean. In the aquarium, it has to be removed.

Why Organics Are Bad

While only a few of the organic compounds are directly toxic to marine livestock, they can stimulate the growth of heterotrophic bacteria which robs your tank of oxygen. These bacteria also create carbon dioxide. The result is lower pH and low ORP, which creates ideal conditions for nuisance algae to thrive. Organics can quickly tint aquarium water to a yellow color which greatly blocks blue spectrum light penetration (actinic 420nm). High levels of organics can also tax a protein skimmer to the point where nitrates and phosphate removal becomes minimal.

No one knows for sure the total make up of organic compounds in the marine aquarium and what specific effects they have on different organisms. It had been observed that aquariums with high organic levels experience more fish and coral diseases. There is now firm evidence that organics stunt fish growth. The old mystery of how a fish will grow only as large as its container has been solved. It has nothing to do with the volume of water or the size of the tank- organics accumulation is the culprit.

At moderate organic levels, corals and invertebrates tend to close or cease reproduction. Some researchers believe that there is a direct relationship between high levels of organics and dense populations of disease organisms. The reduction of naturally occurring organics ultimately leads to improved water quality and healthier specimens. Activated Carbon is the most effective and easiest method of removing organics from aquariums.

How to Tell if Your Organics Levels are High

The tell tale signs of high organics in marine aquariums include (1) Persistent hair algae problems despite low nutrient levels, (2) Some foaming in the sump or in the corners of the tank, (3) An oily film or cloudy layer on the water surface where even a tank overflow can’t seem to get rid of all of it, and (4) small growths of Cyanobacteria spotting on rocks and the gravel.

How Activated Carbon Works

Activated carbon is a unique product that starts out as nut shells, wood, or coal. It is pyrolysed in a 750°C oven which cracks the material and creates millions of micro pores on the surface and though the interior of each grain. The surface area of these pores are immense. One gram of granular activated carbon has 5,300 square feet of surface area. By comparison, a tennis court is 2,800 square feet. It is not only the large surface area of carbon that attracts organics, but there is an electrical charge involved that draws organics to the carbon.

Choosing Activated Carbon

In the aquarium trade, bulk activated carbon is sold in granular and extruded forms. Extruded products appear as pellets and spheres. These carbons are more rugged and can take tumbling in media reactors without breaking apart. They also tend to have less dust. However, extruded carbons have less surface area than granular carbons, so more product will be needed to achieve the same results. Granular carbons are softer and are more dusty. Dust level has nothing to do with the quality or effectiveness of carbon.

There are lots of brands of activated carbons to choose from. The quality ranges from downright detrimental to excellent. Avoid any product that uses the term “charcoal” or “char” in its name. These products are not activated and are limited to removing heavy metals and odors. There are ineffective against organics. They also contain calcium phosphates- which act as a nutrient for algae growth.

Activated Carbon has gotten a reputation of adding or leaching phosphates back into the water. This is only partially true. Activated Carbon can be made in two ways, either by Physical Activation or Chemical Activation. Physical activation used CO2, oxygen, or steam, and contains no phosphates. Chemical activation uses phosphoric acid and zinc for activation. If you buy the latter, then adding carbon will also add phosphates to your water. You are better off not using carbon at all then using a phosphate washed product.

Here’s a guide on what to look for when buying activated carbon:

► Look on the product label for information about the carbon. If the label talks about the carbon process of using steam, oxygen, or carbon dioxide, then it is truly phosphate-free and won’t leach phosphates into the water. Some carbons are simple marked “Phosphate-Free” which indicates a steam activated process. If the label does not mention phosphates, doesn’t tout the activation process, or requires rinsing to minimize phosphates, it is likely a low grade phosphor-washed carbon that should be avoided.

► If you use your carbon in a media reactor or tumbler, buy an extruded or pelletized carbon. It won’t break apart when the grains bang into each other. For use in canister filters or mesh bags, use granular carbon. It will give you more surface area- albeit at the cost of being softer and more fragile.

► Ash is an inorganic material that is left behind after the activation process. Look for carbon that is marked as low ash content or one that states “Does not affect PH”. High ash content can cause a significant rise in PH when first placed in the aquarium. This can cause undue stress on the livestock. I have personally seen pH values climb within minutes from 8.0 to 9.5 pH with some carbons. All carbons contain some ash and a thorough rinsing in fresh water will remove most of it.

► Quality brands of activated carbon will feature other parameters, such as Iodine Number below 600, Molasses Number above 400, or listing pore size in Angstroms. These are all signs of a quality manufacturer that has nothing to hide, and is offering a superb product.

BRAND	Average	Good	Excellent
Aq Pharm Black Magic®	█
Kent Reef Carbon®		█
Boyd Chemi-Pure®			█
Hagen® Fluval® Carbon			█
Hydor Prime®	█
Lifegard® Pelletized	█
Marineland Black Diamond®		█
ROWAcarbon®			█
Seachem Matrix®		█
T.L.F. Hydrocarbon®			█
Warner® Granular			█

How To use Activated Carbon

► For ongoing maintenance, I recommend 1 cup per 60 gallons of water. This is a bit higher than most suggestions, but using more carbon works faster and lasts longer. Double this amount for tanks with obvious signs of high organics or first time carbon use in poorly maintained tanks.

► Filter the water mechanically before it reaches the carbon. Particles greater than 100 microns in size will take a toll on the life of the carbon.

► Despite popular belief, carbon does not need to be placed in a canister filter or a compartment where all tank water passes through it. Dropping a mesh bag full of carbon into the sump works fine. This is because carbon works by electrically attracting particles- it is not an inert mechanical filter. Studies have shown that bags of carbon in a sump with moderate flow removes substantial quantities of organic pollutants, medications, and heavy metals. Actual performance depends on the flowability of the bag material. It is most effective if you use a media bag with the largest possible hole sizes but small enough where the carbon cannot escape.

► For the average marine fish aquarium, carbon will last 6 weeks. Reef tanks produce more organics than fish-only tanks, so 4-6 weeks is a workable limit. If the water is not mechanically filtered or the aquarium shows signs of nuisance algae, you will need to adjust the useful life or increase the amount of carbon.

► There is no effective way for the aquarist to either recharge carbon or measure its rate of exhaustion. I have experimented with the Salifert Organics Test Kit to measure carbon life, but I was unsuccessful because the range of the test kit would not allow me to measure steady declines over time. Don’t re-use carbon or try to clean it. Recharging carbon requires a specialized high temperature/low oxygen oven that would be prohibitively expensive at this small scale. The best solution is to replace the carbon at 4 to 6 week intervals.

Activated Carbon Myths and Misconceptions

► Carbon removes trace elements- Carbon has a greater affinity for organics than trace metals, but it will remove some trace elements. On the other hand, both protein skimming and natural consumption of trace elements by tank specimens will remove significantly more trace elements than carbon. Aquarists concerned about depleted trace elements should be using a trace mineral additive- whether or not carbon is used. Two excellent products for this are the Sera Strontium Complex and the Seachem Reef Trace products.

► Carbon will leach organics back into the water False. Once all the carbon pores are saturated, bacteria slime and detritus will accumulate on the carbon grains, turning it into a weak biological filter with the organics locked in the deeper layers.

► Carbon should be used only a few days a month False. This myth was likely started by activated carbon’s ability to remove yellow tinting and odor from the aquarium within the first 48 hours of application (or perhaps manufacturers who want to sell you more carbon). The higher concentrations of organics are colorless and odorless and require more contact time for removal. Another complication of part-time carbon use is storage and reuse. Once the carbon is removed from the aquarium it will continue removing contaminants from the air. Placing the damp carbon in a sealed plastic bag doesn’t work either, as the damp carbon becomes exhausted servicing die off in the stagnant aquarium water stuck to the grains.

► Spilled carbon causes harm to the aquarium False. Carbon granules that are accidentally spilled into the aquarium will quickly become saturated with bacteria slime, having the same biological effects as a grain of gravel. It may look ugly, but it is totally harmless.

As we have seen, the use of Activated Carbon is an important part of maintaining a healthy marine or reef aquarium. It is the only filtering media that can remove substantial amounts of metabolic wastes (organics), which accumulate over time and can prevent secondary water quality and health problems in specimens. Because of the phosphate issue in lower quality products, it is better to spend a little more on a quality carbon than use any carbon at all.

 

This is a follow up to my previous blog of November 2007 concerning nitrates. I presented an article all about Nitrates- where they come from and how to deal with them. I discussed deep sand beds, live rock, coil denitrators and chemical additives such as AZNO3. All of these methods (or a combination of them) can be effective in reducing nitrates in the aquarium. Nitrates are the number on cause of algae in marine and reef aquariums, and some form of algae control is mandatory for long term success.

But the problem with all these methods is that they require high maintenance by the aquarist on a continuous basis.. Deep sand beds need cleaning, Live rock needs to be “turkey-basted”, coil denitrators need to be fed, and chemical additives need to be dosed daily. Some people take the “after approach” of using snails or herbivorous fish to eat the algae that is caused by high nitrates. Same problem here: snails have short lifespans and need to be replaced frequently. Herbivorous fish may suddenly lose their taste for certain algae types with no apparent reason.

At the end of the orginal article I touched on a new method of nitrate control (new to the hobby, but used extensively in public aquariums). It is called the Sulfur Filter. It also goes by the names Nitrate Reactor, Sulfur Denitrator, or Sulfur Reactor. This device looks very promising because it is virtually maintenance free and is designed to remove large quantities of nitrates in a small footprint. Heavily loaded tanks with 100+ ppm of NO3 can easily be maintained at zero or unmeasurable levels.

When this article went to press back in November 2007, I has no personal experience with sulfur filters. Eric Edwards of Fins and Reefs (www.finsreef.com) saw the article and sent me a unit for testing. This particular model is an H&S 110SR, rated for use up to 250 gallons.

Before I get into my findings, let me explain how these things work. They look and work very similar to a calcium reactor, but require no CO2. The chamber is filled with pure elemental sulfur in the form of small bright yellow beads. The nitrate removal mechanism is called “Autotrophic Denitrification by Sulfur-Oxidizing Bacteria”. Now that’s a mouthful. The process though is quite simple.

The bacteria species that do all the work are Thiobacillus denitrificans and Thiomicrospira denitrificans. You don’t need to add this bacteria to start the filter. They are all over the planet and exist everywhere, including in your aquarium water.

Tank water is pumped into the bottom of the filter at a very slow rate, like 1 drop every 1-2 seconds. The water pushes upward through the sulfur beads and the oxygen is stripped out by bacteria. The higher up you go the less oxygen is present. The bacteria in the upper layers have no oxygen to use so in order to survive, they need to create it themselves. They do this by eating the sulfur and combining it with nitrates (and also nitrites, if present) which liberates an oxygen module for food and in turn, gets rid of the nitrate molecule. The water leaving at the top of the chamber is nitrate free.

There are some side effects to this process. Nitrogen gas is produced, which is no big deal as it just escapes out the top of the chamber. Carbon dioxide gas is also produced which is a big deal. The water leaving the chamber is very acidic and will lower your pH. To fix this, a layer of calcerous material (like crushed coral or aragonite gravel) is placed on top of the sulfur beads. This process also adds sulfates to the tank water, but the quantities are so low that an imbalance is unlikely.

All aquarium sulfur filters use a recirculating pump. This increases efficiency by passing tank water through the sulfur multiple times before it exits. Also, very little sulfur is consumed, so you won’t have the replace the sulfur media for 3-5 years.

This all sound wonderful, but does it really work? I had my doubts. Here’s what I found out.

 

I hooked the H&S 110R to a 125 gallon FOWLR tank. This aquarium has 12 large fish in it (around 3-7 inches long) and around 40 lbs of live rock. Nitrates have been as high as 50ppm, but due to aggressive skimming and regular water changes I was able to keep it down between 25 and 30 ppm, albeit with a lot of effort. The aquarium exhibited the usual algae signs for this level of nitrates- I need to clean the front glass 2-3 times a week, and tufts of hair algae appear from time to time here and there.

The directions that came with the sulfur filter said to start the drip rate at around 1 drop per second, and in two or three days check the nitrate level in the drip water. If it’s not zero or close to zero, then slow down the drip rate some more. Well, in 3 days the nitrates were 25 ppm, the same as the tank water. I did slow down the drip rate as slow as I could go, maybe one drop every 5 seconds. But the problem is these little airline valves are crappy. I’d wake up in the morning and it wasn’t dripping at all. I had to fiddle with it all the time.

I waited two weeks for the filter to cycle and checked nitrates again. The level was around 20 ppm. I tested both the drip output and the tank water and they both read the same. I couldn’t figure out why that would be. So I gave it another two weeks.

After running it to the end of the month, the nitrate was level was around 12 ppm. This thing is definitely working, but not the way I expected. Same deal on the nitrate testing- both tank and output drip read the same.

I let another month go by. Measured the output again. Still at 12ppm. Perhaps I reached the capacity of the unit- this is all it could handle. This aquarium gets the equivalent of 4 frozen fish cubes a day in food, so maybe it just can’t keep up with that. I kinda expected the break-in period for sulfur filters to be like cycling a new aquarium. You know, ammonia, then a continuing nitrite rise for a month, then a nose dive to zero. Not the case here.

When I hit 2 months the results were still the same. Maybe the nitrates dropped just a little to around 10 ppm (it’s hard to read the colored liquid against a printed paper color on these test kits). Anyway, I called Eric at FinsReef to talk about this. He was a bit surprised at how long it was taking, but emphasized that the H&S 110SR could easily handle my tank with room to spare. He told me that the cycling time runs differently on different aquariums. Tanks with higher initial nitrate levels seem to cycle faster. But sooner or later, they all kick-in. He suggested flushing the sulfur filter by running the output full open for a day. Perhaps some CO2 or other gases or contaminants were preventing the unit from fully working. Also, adding some vodka (1ml every two days per 75 – 125 gallons) will provide a carbon food source and speed the cycling.

I took his advice and did all of that. I also unplugged my UV sterilizer. Maybe the UV unit is killing all the bacteria in the water before it settles on the sulfur beads. Eric didn’t think the UV sterilzer would have any effect, but I unplugged it anyway.

Another week went by. Still the same results. At this point I convinced myself that this was as good as it gets. But not too shabby- I could never get nitrates down to 10 ppm using water changes and skimming alone. So I was satisfied, but certainly not a believer in all the hype on how well these filters work. I also used the last of my nitrate test kit chemicals, so rather than run out a get a new test kit, I felt that this experiment was over.

The following week things started to change. It was Wednesday and I didn’t need to clean the front glass of film alage. The gravel, which was always covered with a little bit of brown and green algae, had areas of white showing through. Over the next week, the entire gravel bed turned white and all the algae died. My hair algae was gone except for a patch stuck on a powerhead. I pulled that off with my fingers which left a bunch of short strands still attached. Within a few days, even those strands died off. My tank never looked better.

I still haven’t replaced my nitrate test kit but at this point, I felt I didn’t need to. I don’t care if nitrates are at zero, 10 or 20 ppm. The result I was looking for is there.

I really don’t know if turning off the UV unit, flushing the sulfur filter, or adding the vodka was the fix. Or perhaps it was none of these- it was going to take 3 months to cycle no matter what I screwed around with. I tend to believe the latter is what really happened here.

My recommendation? You’ve got to go out and get one of these for yourself. Forget about deep sand beds, deniballs, and nitrate removers. This is the way to go.

I didn’t test the sulfur filter on a reef tank yet, and I will probably do that in the next month. A reef tank normally has far less nitrates than a FOWLR, so the effects may not be as dramatic. But the biggest advantage I see of using one of these on a reef tank is getting away with more frequent feedings. If I could achieve daily feedings in my reef tank with little or no algae growth, then in my opinion, the sulfur filter is worth its weight in gold.

Here’s a recent presentation I did on how to create interesting and functional aquascaping in any reef, FOWLR, or mixed marine aquarium.

aquascaping.wmv

Turning Aragonite into Concrete

A few years ago I decided to redo my 125 gallon FOWLR tank. My goal was to come up with a more attractive aquascape, including adding some more live rock. Over the years I added a bunch of stuff to my sump. A larger skimmer, a small refugium, a powerhead, a filter sock, the list goes on. At this point, the sump was a plumbing and electrical cord nightmare. So I figured while I was at it I would redo the sump as well. As most of you know, aquarium stands are not sump-friendly, so I would need to drain the tank down and pull it away from the wall a bit to remove and redo the sump. I put all the fish in a holding tank, drained the water into several Rubbermaid trash cans, and was ready to start the job.

 

After I got all the live rock out, I would replace the gravel with some new bright-white Aragonite. To my dismay, I started to scoop out the gravel and found it was a solid sheet. All of the gravel was cemented together. It was incredible. I tried to break it apart with my hands, and aside from being very sharp It was very heavy. I wound up using a hammer inside the aquarium, whacking the gravel sheets and breaking them up so I could take out manageable chunks. What’s going on here?

My first thought was that bacteria slime was responsible for welding the gravel grains together. I decided to experiment. I soaked a piece of the gravel rock in bleach overnight. The next morning, nothing was different. It was still a rock. I thought about putting it in a low pH solution like Muriatic acid. But the gravel grains themselves would dissolve and I would likely wind up with a bucket full of Alka-seltzer.

So I checked my reef aquarium for the same condition. It was seeded with gravel from the FOWLR tank. The gravel in there was normal and loose. I mentally went through a list of the difference is these tanks. The reef aquarium had a calcium reactor and the FOWLR didn’t. If anything, I would expect that the calcium reactor could be the cause, but the exact opposite was happening. I drip Kalkwasser in the FOWLR and not the reef, and this was the major difference. I browsed the Internet for posts about this problem, and found many, many aquarists complaining about gravel clumping after starting a limewater drip. I was curious why this is happening. No way can Kalkwasser add as much calcium and carbonates to an aquarium as a calcium reactor. I dove a little deeper into some technical papers and what I found was both the cause and a cure for gravel clumping.

First, a little background. Aragonite is the most popular gravel used in saltwater aquariums. It is made up of mostly calcium carbonates and strontium. It’s created by once living creatures. This gives it a special structure or matrix at the molecular level which causes it to dissolve at a high pH. Aragonite has an equilibrium of 8.2 pH. This means that if it’s submerged in water with a pH lower than 8.2, it will start to dissolve. In reality though, any major buffering effects for a saltwater aquarium really don’t take place until the pH is around 7.7 – 7.8 pH.

Calcite is another gravel sold in the aquarium trade. Commonly called limestone, it is composed of near pure calcium carbonates. However, unlike Aragonite it is created chemically by sedimentation, heat, and pressure. It is mined and crushed into gravel. It’s molecular structure is quite different than Aragonite. As a result, it has an equilibrium of 7.6 pH. It has practically no buffering effects for marine aquariums. Your pH would have to drop to 7.1 before it starts really working. A word to the wise: If you buy calcite gravel for your aquarium, you might as well just use silica sand because neither will buffer anything.

The Mechanics of Clumping

Everyone sets up a new marine aquarium pretty much the same way. You add your gravel to the dry tank, then either add saltwater mixed elsewhere or add fresh water and dump in the salt. In this sterile, chemical soup, a lot of calcium precipitation is happening. All Aragonite gravel grains that are touching one another form a thin layer of calcium carbonate precipitant which is- you guessed it, Calcite. This layer gets thicker as the weeks and months go on, cementing the gravel grains together.

The higher the pH, the more Calcite is formed. Folks who start dripping Kalwasser in their tanks (especially those with low pH to begin with) aggravate the situation. The calcite grows like gangbusters. And Calcite isn’t going to dissolve in your aquarium- the pH is too high for that.

So does Kalkwasser drips causing clumping? No. It is actually the beneficial, higher pH side effect of Kalkwasser that accelerates Calcite formation. But I don’t recommend stopping Kalkwasser to fix this problem because it is one of the best things you can do to maintain any saltwater aquarium. So what’s the fix?

Bacteria slime to the rescue! This is a slippery organic film that eventually covers all surfaces in an aquarium, including all grains of gravel. It blocks the formation of Calcite on the gravel grains. This prevents Calcite from acting as an Aragonite cement. The reason why my reef tank showed no gravel clumping was because 100% of the gravel came from a seeded tank, which was fully “slime-covered”. So the trick to eliminating gravel clumping is to use aged, slime-covered gravel instead of the sterile stuff fresh out of the bag. While most of us use a little “seed” gravel from a mature aquarium to start a new one, it’s pretty hard to find 50 pounds of seeded gravel laying around. But you can easily make your own.

 

 

Depending upon the quantity you need, get a plastic storage bin from the Dollar store or use a trash can and fill it with fresh gravel. If you already have another marine aquarium going, fill the container with used seawater from a water change. If you don’t have another aquarium, your aquarist friends will gladly give you all the used seawater from their water changes.

Place an airstone in the bottom of the container to supply oxygen. Feed the container with anything you have on hand like powdered or wet filter feeding foods, apple juice, etc., anything will work. Let it run for 3 weeks, feeding once a week. It’s also a good idea to stir it it up a bit during this time. At the end of three weeks you will have gravel that I guarantee won’t clump. In addition, it will accelerate the cycle time for your new aquarium setup.

The Selection, Care, and Feeding of RO/DI Filters

As the marine aquarium hobby advances to more and more delicate creatures, we have become aware that the source water we use for salt mixing and top-off plays an important role in the health and cleanliness of our tanks. The RO/DI (Reverse Osmosis, De-Ionizing) filter has become an essential piece of equipment in keeping saltwater aquariums.

I bought my first RO/DI filter in 1989. In those days, they were sold mainly through laboratory supply catalogs and companies that specialized in water purification equipment. There wasn’t a big demand even in the aquarium hobby, because keeping delicate corals and other organisms was in its infancy.

 

The unit I bought was a 10 GPD (Gallons Per Day) RO unit with a CTA membrane for $450. That did not include the DI filter, which was this dual cartridge monstrosity with separate anion and cation chambers. If I recall, that was another $250.

Today, RO and RO/DI combination units are sold everywhere and at prices for every budget. During the 1990’s, the public exposure of contaminants and carcinogens in the nation’s tap water made everyone aware that tap water may not be fit to drink. This was a boon for water purification companies. Industrial and laboratory products were down-sized and cost reduced for the general public. Today, you can purchase a 75 GPD RO/DI filter system for as little as $125. But like all things made for the consumer, there are quality products and cheap junk sitting side by side on the shelves. Choosing an RO/DI filter requires the same decisions and trade-offs as buying any other piece of aquarium equipment. If you already own an RO/DI unit, keeping the effluent water as pure as the day you bought it will take maintenance. A TDS (Total Dissolved Solids) meter helps, but it is not the total picture.

Why buy a Reverse Osmosis system or use RO/DI water in the first place? It all boils down to two things: algae and toxins. Municipal and well water supplies all contain fertilizers. No matter where you live, the water you drink in your home is pumped up from parts of the subterranean water table and for municipal supplies, it is combined and stored with surface water in reservoirs, streams, and lakes. Fertilizers get into the water supply from lots of places. Water treatment plants concentrate on human bio-hazards by removing bacteria and viruses before it gets to your faucet. Dissolved fertilizers (like nitrate, phosphate, potassium, silicates, and iron) are kept at federal standards, which are hundreds of times higher than the acceptable range for an aquarium. The result of using unfiltered tap water for top-off and salt mixing may be an aquarium with uncontrolled algae, excess detritus, and unexplained die-off from industrial toxins. These pollutants not only make your aquarium hard to keep clean, but it robs your tank of oxygen, lowers pH, and directly smothers and kills even the smallest bacteria and organisms. Water changes don’t help, in fact they make things worse because some nutrients may have been naturally lowered by the beneficial bacteria in your aquarium. Doing a water change raises nutrients levels back up again.

The second reason for RO is to eliminate toxins. Probably the worst offenders are copper and lead. Copper is a well-known natural bactericide. 17^th century shipping vessels used to nail copper sheets to the hulls of their ships to prevent barnacles and other sea life from attaching to it and causing drag. Even modern US Navy ships use copper fibers mixed into hull paints. The EPA allows drinking water to contain up to 1.0 ppm of copper. Forget about corals and inverts- at this level all your fish will die too. Fortunately, most of the country has far less copper concentrations than this. But if your house has copper pipes, you may well be adding additional copper. Blue stains in your sinks or toilets is an indication of high copper levels. If your tap water has a high pH you may not see the blue stains, but you could still have lethal aquarium levels.

There are many other toxins in tap water most of which are manufactured chemicals that, despite EPA regulations, wind up in well and city waters. Things like Trihalomethanes, Chloroform, and Bromodichloro-methane. Many of these compounds are carcinogenic to humans, and no one really knows their effect on corals, invertebrates, or fish. In my opinion, you really don’t want this crap in your tank.

 

How RO Works

Before I explain reverse osmosis, let me try and explain regular, plain old osmosis. The term osmosis has been traditionally used to describe organic, semi-permeable membranes like the lining of your stomach. But here’s a better example. You’ve probably heard of a fabric called Gortex, They make jackets and clothing out of this stuff. It is a waterproof fabric, so rain just runs off of it. But it also allows water vapor (like your sweat) to escape though the fabric. This is osmosis in action. Gortex is full of sub micron holes that stop water from penetrating, but allow smaller water vapor molecules to pass right through it.

Suppose we reverse the action of Gortex? Instead of stopping rain and letting water vapor pass through it, we do the opposite. We use a high pressure supply to force water against the fabric and what we get out of the other side is water vapor.

Reverse Osmosis filter membranes work in the same way. Normally, ultra pure water will slowly permeate all by itself and pass through to the dirty water side of a membrane. The holes are too small for the dirty water to flow back. With RO, we apply pressure on the dirty side and in the process we make pure water by forcing the flow backwards or reversed across the membrane.

The holes in an RO membrane are roughly the same diameter as water molecules. So anything bigger than a water molecule (like a sodium or a calcium molecule) are too big to pass through the holes. However, other elements like silicates, ammonia, and hydrogen sulfide are very small and will freely pass through. Living organisms such as viruses and parasites are also blocked, because the size of these creatures are hundreds or thousands of times larger than a water molecule.

After a very short period of time, all these big dirty molecules start to cake up on the dirty water side of membrane and it won’t allow the pure water molecules to freely pass through anymore. The membrane has to be washed off constantly to prevent clogging. All RO units contain a built-in backwash system, which sprays water on the membrane to wash off all that junk. This is called the waste water system. On the average, it takes about 5 times more water to wash off the membrane then the amount of pure water that can pass through the holes.

 

The Complete RO/DI System

You can’t just hook your faucet to an RO membrane and be done with it. The membrane itself is very thin and fragile and tears easily. If you’ve ever seen an RO membrane, it looks like a piece of Saran Wrap, except maybe a 100 times thinner. You can’t see any holes in it. To protect the membrane from damage and short life, the feed water must be prepared before it reaches the membrane.

There are several steps to get water in and out of an RO/DI system. The first step or stage, is to filter out really big particles in relation to the membrane holes. What is normally used for this is a 1 micron mechanical filter called the sediment filter.

The next stage is a carbon block filter. The carbon filter has three jobs. The first is that carbon block filters are also mechanical filters, which further reduces particles down to around 0.5 microns. Secondly, they removes certain organic compounds, some of which will pass through the RO membrane. Third, it blocks chlorine and chloramines. Think of chlorine molecules as little baseballs covered with razor blades. They fly at the RO membrane and cut it to shreds. If you let chlorinated water near your membrane, it will ruin it.

Chloramines are even worse- they are a tight bond of chlorine and ammonia, two substances that you never want in your aquarium. If you fill a glass with chlorinated tap water, in about an hour all the chlorine will dissipate naturally and escape into the atmosphere. With chloramines, the same process will take 2 weeks. So without a carbon filter (or just as bad, your carbon filter is exhausted), your membrane won’t last very long.

Water from the carbon filter now flows directly into the RO membrane. Their is also another couple of connections in the housing to support the washing process. The membrane itself is spiral wound to increase surface area and is combined with other separating materials to facilitate the washing process and even flow. The flow restrictor in the waste water tubing is what sets the ratio of waste water to production water. Most units are preset to a 4-5 times ratio of waste water to the GPD rating of the membrane.

After the membrane the water flows through the de-ionization cartridge. Here, synthetic resin beads have negative (cation) and positive (anion) charges which attract and trap various contaminants from the water by electrical charge. Note that some molecules do not have an electrical charge (like water itself, nitrogen, oxygen, and chloramines). They pass straight through the DI cartridge. Things like copper, lead, silicates, phosphates, and sodium have strong electrical charges that are all trapped in the DI resins.

Finally, the production water goes to the pressurized storage tank. Here is where the RO water is stored until you need it. The automatic shutoff valves stops RO water production when the pressure tank is filled, which is typically around 40 psi. From there, the water goes through a carbon post filter then to the faucet or outlet where RO water comes out at near full tap water pressure, at least until the pressure tank is empty.

 

Tips for buying an RO/DI unit

You can buy an RO/DI filter just about anywhere, from Home Depot to Sears to mail order fish supply houses. The prices vary all over the map as well as the quality. By quality, I don’t mean the physical construction of the unit but rather the water production quality. Here’s some things to look for when shopping for an RO/DI system:

Clear Housings – Always get a unit that has clear filter housings. You will need to check your sediment filter visually at least once a month. An opaque filter housing just won’t work. Clear housings are also made from hard polycarbonate versus molded PVC. They can take a lot of abuse in terms of thread wear, which prevents drips and leaks over time. Clear housings are more expensive. A company that only offers opaque filter housings may be a sign of other inferior components in the rest of the RO/DI system.

Internal Flow Restrictor – Quality units have an internal flow restrictor that are mounted in the membrane housing and run down inside of the waste water tubing. (This is why you should never cut or shorten the length of the waste water pipe- you will cut the capillary tube of the restrictor). Units that have an external restrictor built from pvc pipe are not as accurate and produce more waste water.

Filter Housing Size- Never buy an RO/DI unit that uses proprietary or custom size filter housings. The standard water cartridge size is 10 inches. If you get anything else, you will only be able to buy replacement filters from the original manufacturer.

RO Membrane- This is the crux of the entire RO/DI system. Ironically, it is also the most difficult item to compare when shopping around. This is because RO/DI makers don’t generally publish the makes and models of the membranes they use. Mass market RO/DI systems use the Dow Chemical FilmTech light duty residential TFC membrane. The very low cost of this membrane has enabled everyone and his brother to sell RO/DI units. Yes, it works, but keep in mind that it was designed for low cost and frequent replacement.

 

There are many different types of RO units available with different membranes. Never buy a unit that uses a CTA (Cellulose acetate/triacetate blend) membrane. This is old technology with limited useful life and lots of problems. Stick with a TFC (thin film/thin layer composite) membrane. These have very good rejection rates and a longer life, but can be destroyed quickly by chlorine or chlorimines in the feed water.

While there are only a handful of membrane manufacturers, each one offers hundreds of products with varying degrees of quality and cost. You can buy a membrane that will completely desalinate sea water, or one that can barely remove trace amounts of copper. The only way to know for sure is to purchase your unit from a reputable manufacturer.

I recommend Spectrapure (www.spectrapure.com) as the best source for both RO/DI systems and replacement parts. The company hand tests and sorts their membranes for flow and rejection, offering a variety of membranes from 95% to 99.9% rejection rates.

Saltwater aquarists need large amounts of water periodically for salt mixing. You can add on another pressurized storage tank to any RO/DI unit. You can also use an open container like a Rubbermaid trash can to store water. In the latter case, don’t be surprised if you read 5 ppm or more TDS in the trash can. Airborne dust and dirt as well as bacteria slime growing on the sides of the container quickly accumulate.

The GPD rating is not set in stone. One manufacturer may claim 100 GPD performance, while the exact same membrane will be rated at 60 GPD by a manufacturer with a more conservative (and realistic) specification. For most hobbyists managing up to 250 gallons of saltwater, a 50 to 60 GPD unit will be more than adequate. While it is certainly nice to make RO water faster, the negative side of this is that water passes too quickly through the DI cartridge, reducing the dwell time.

 

Getting the Most out of an RO/DI System

The number one complaint by RO/DI owners is water production. It is not uncommon to buy a 75 GPD unit and barely make 25 GPD. Here’s why. A membrane may be rated at 80 psi but your tap water pressure is in the range of 40 to 45 psi. That alone will drop your water production rate to 41.5 GPD. Add in the fact that most membranes are rated at 25C (77F). The warmer the water, the more efficient the unit. Unless you live in the desert, your tap water temperature is in the range of 50F to 60F. This reduces GPD by another 30%. Now our 75 GPD unit is down to 27 GPD. Each 100 ppm of TDS reduces the flow further by 1 psi. The combination sediment and carbon block filter has at least 2 psi back pressure when the cartridges are brand new, so that accounts for another 3 psi drop. The 75 GPD RO/DI system is down to a realistic 24 GPD.

Despite these drawbacks, there is a lot you can do to maintain good water production rates:

Replace Your Sediment Filter- This filter needs to be replaced more than any other. Fortunately, it is also the cheapest filter cartridge to buy and costs around $5. All RO/DI units should use a 1 micron sediment filter. Don’t be tempted to go to Ace hardware or Home Depot and buy a 5 or 10 micron cartridge as a replacement. Doing so will clog your carbon block filter, which costs more to replace and will slow your water production.

There is no preset number of gallons when to replace the sediment filter, because incoming sediment varies by water source. As a rule of thumb, replace the sediment filter every 4-5 months. The best way to check the sediment filter is visually. If it looks yellow or has light brown patches on it, it’s definitely time for replacement. I have a high amount of iron in my tap water, so my sediment filter clogs and turns yellow in about 3 months.

Carbon Block Filter- You need to stay on top of replacing this filter because carbon has a tendency to leach contaminants back into the water when saturated. If you’re on city water treated with chlorine or chloramines, it’s even more important because chlorine will quickly destroy your RO membrane. Aside from being a chemical filter the carbon filter is also a 0.5 micron mechanical filter. They do and will clog over time, slowing down water flow to the RO membrane. Without chlorines present, I would recommend changing the carbon block filter every 500-700 gallons or every six months, whichever comes first. With chlorinated tap water, the more often the better. keeping a 500 gallon limit is prudent in preventing membrane damage from a chlorinated water supply.

RO Membrane- The most expensive item to replace. The RO membrane accounts for 50% of the cost of an RO/DI System. You want to protect the membrane at all times, and replace the prefilters (sediment and carbon block) frequently. With good maintenance practices, the membrane should last from 3 to 5 years. Though If you have high TDS (Total Dissolved Solids) source water or don’t replace your prefilters often enough, 2 years may be a practical limitation.

You can measure your rejection rate and ongoing life of your membrane with a TDS meter. These meters are nothing more than conductivity sensors, measuring how much electricity flows through minerals dissolved in water. They are relatively inexpensive- a dual TDS meter can be had for less that $30. Most people mistakingly hook up dual TDS meters at the raw (tap water) intake and the final output of the DI cartridge. This doesn’t give you the information you need to properly monitor the system. It is much better to measure across the RO membrane. That is, after the prefilters and before the DI cartridge.

A healthy membrane will reduce TDS from 10 to 100 times. For example, if you have 200ppm TDS reading at the input to the RO membrane, the membrane is working as long as the effluent remains below 20 ppm. This is also how you measure your rejection rate, which is the efficiency of the RO to remove contaminants.

You can figure out your own rejection rate. Rejection rate equals input water TDS subtracted from output water TDS divided by input water TDS. So for example, if your input water is at 200ppm and the output of the RO is 5 ppm you have a 97.5% rejection rate. You need to stay between 95% and 99% for peak performance. Let’s say the output TDS rises to 20 ppm after a year. Now you’re at a 90% rejection rate which is way too low. You will need to replace your RO membrane.

Over time, all membranes lose the ability to maintain rejection rate. They get clogged up with deposits, bacteria slime grows on them, and they just get torn up. You can’t rely on the DI cartridge to compensate for this, because the RO membrane and the DI cartridge removes different things.

A common mistake is to replace the DI cartridge when TDS levels in the final production water (output of the DI filter) goes above zero. In some cases the problem is a damaged or old membrane. Another indication is that your DI cartridges don’t seem to last very long. Using a membrane with a low rejection rate overwhelms your DI cartridge to the point where it can’t keep up.

DI Filter- Most RO/DI systems come with a 50/50 mixed bed de-ionizing cartridge. While this general purpose mix may work for most of the country, I live in Western North Carolina where the soil contain large amounts of Mica (crystallized silicate) and clay. These form other hard-to-remove silicate compounds like Botite and Lepidolite. Iron is also in abundance here, which acts as a catalyst for photosynthesis and fuels algae growth. I need extra measures to remove silicates from my source water (note: RO membranes don’t remove any silicates). I purchase DI replacement cartridges that have resins that favor higher silicate removal.

A TDS meter is a great tool to measure both RO membrane and DI cartridge life. Unfortunately, the reading tells you only the amount of dissolved solids, but doesn’t tell you what is dissolved. If you’re reading 5 ppm out of your DI cartridge, it could be 5ppm of Calcuim which is good, but if its 5ppm of silicates or iron, it’s bad. Some people replace their DI cartridges on any reading above zero. Others shoot for a 5 or 10 ppm maximum. In my locale, any reading at all is likely heavily weighted towards silicates, so I’m quick to replace my DI cartridge on single digit TDS readings.

 

More Water and Less Waste

The two things everyone wants out of their RO/DI system is more pure water and less waste water. There are several things that can be done to achieve these goals:

Pressure Pump – The efficiency of line powered RO/DI systems are at the mercy of your tap water pressure. The higher the water pressure, the more water you can make which in effect lowers waste water. Some RO/DI units come with a booster or pressure pump that pushes more water against the membrane. You can also buy an add on pressure pump for your existing system. The pressure pump increases water pressure against the membrane to around 75-80 PSI. Of all the things you can do to enhance production and decrease waste water, this will have the most impact.

Warm Water – Water production declines rapidly with cold water. Some people hook their feed water to the hot water lines. This is a little dangerous because most RO membranes are rated to 100F maximum. On the other hand, the feed water flows pretty slow and it may have a chance to cool down before it enters the unit. Another alternative is to use a long coil of tubing on the input, which will warm the incoming water near room temperature before entering the membrane.

Restrictor Tweaking – The waste water restrictor has a fixed discharge rate that has nothing to do with the amount of RO water you make. For example, A 75 GPD RO unit produces 375 gallons of waste water per day, even if all you get out of it is 10 gallons of RO water a day. The flow rate of the restrictor is sized to protect the membrane in very hard water. If you have soft water, you can reduce the amount of waste water substantially. Mixing restrictors and membranes yourself is tricky business. Reputable companies like SpectraPure can assemble an RO/DI unit for you that minimizes waste water based on the hardness and pH of your tap water.

Color Changing DI – If you have a TDS meter there is no reason to buy a color changing DI resin cartridge. These cartridges contain inert beads that do a one time color change based on dissolved solids. They take up room in the cartridge that would otherwise be used for DI resins.

 

Alternatives to RO/DI

Because of the large amounts of waste water produced, many people look for alternatives to RO/DI systems.

A superior solution is a portable distiller. The purity of the output water puts RO/DI to shame. You can submerge a toaster in a sink full of this water and the heating wires will continue to glow red. Distilled water is used to put out electrical fires. It is the closest thing you can get to 100% h₂O molecules. The drawback is portable distillers are expensive. A 50 GPD distiller will run about $1300.

If your tap water consists mainly of calcium, magnesium, and other aquarium-harmless minerals, then the Poly BioMarine Kold-Steril unit may work for you. It consists of a sediment filter and a stack of Polyfilters followed by a DI Cartridge. This system will remove heavy metals and organics, but does not remove other dissolved solids. It also requires frequent DI cartridge replacement.

Instead of buying your own RO/DI unit, you can purchase RO/DI water from dispensing machines found in front of large grocery and department stores. For those with one or two small aquariums, this might be a good solution. My only concern with these machines is their maintenance schedule. You don’t know how often the DI resins or membranes are serviced. If you know someone with a TDS meter, take a reading of the water and if it is less than 5ppm, it should be okay.

Another alternative is buying distilled water at the grocery store. But be careful here- if the fine print on the label says “distilled through deionization” you are essentially buying RO/DI water at a premium. If you find yourself buying more and more machine or bottled water, figure out your total costs and decide when it makes sense to switch over to your own RO/DI system.

No matter what your water source, it is becoming more difficult to use straight or lightly filtered tap water in any marine aquarium. An RO/DI system is the best bang for the buck when it comes to maintaining your marine and reef tanks. It will minimize the growth of algae and keep dangerous toxins out of your aquariums.

When most aquarists hear the word nitrates, what usually comes to mind is the whole “nitrogen cycle” thing. You remember this. Your fish take a poop and it breaks down into ammonia. Then the Nitrobacter and Nitrosonomas bacteria take over (which by the way, there is new evidence that proves these strains are NOT the ones responsible for the nitrogen cycle, so all those old books are now wrong). Ammonia is then converted to nitrite then finally to nitrate where it slowly accumulates and provides food for algae, turning your tank into a green mess.

Without any controls, nitrates go nowhere- they just accumulate. When concentrations hit 5 ppm or more, it can fuel film algae, hair algae, and cyanobacteria. In a reef tank, stony coral branches and polyps usually get covered by hair algae strands and film algae. This will harm and often bleach out sections of the coral. It’s not that grave of a situation in a fish-only setup because most marine fish can tolerate higher levels of nitrate. But you will still wind up with unsightly algae growing everywhere.

Not all the nitrates in your aquarium comes from the nitrogen cycle. Nitrates are added with food and with water changes. Many organisms in your aquarium produce nitrates directly. This has nothing to do with the nitrogen cycle.

Nitrate levels in aquariums are much higher than those in the ocean. The average nitrate levels of the ocean is 0.1 ppm at depths up to 50 meters, and 2.5 ppm and higher in deeper regions. But in the South Pacific reefs where we get most of the creatures we want to keep, nitrate levels average around 25 ppb (that’s parts per billion) which is equivalent to 0.025 ppm. So here’s the first problem: a typical hobby nitrate test kit can only go down to about 1.0 ppm, which is a nitrate level 40 times higher than what we’re shooting for. If you test for nitrates and the test vial looks crystal clear and colorless, your nitrate level could still be a hundred times higher than the ocean levels.

 

Why Nitrates Are Bad

Aside from getting nuisance algae, nitrates are not healthy for fish or in