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.