Posted by: joejaworski | 19-May-14

The Right Way to Use 2-Part Additives

Nearly 20 years ago a company called E.S.V invented a product called B-ionic. This was a product that came in two bottles that replenished both calcium and alkalinity in their natural, ionic balanced quantities. The product represented an important milestone in marine aquarium husbandry. Since then, every major aquarium additive company has jumped on the bandwagon and now sell what is commonly known as a 2-part additive.

So what is ionic balance? In simple terms, it means that a given container of saltwater contains just the right amount of calcium at a given alkalinity level. It is the optimum level where calcium consuming livestock can absorb and use calcium for growth.

Calcium and alkalinity interact with each other. When calcium goes up, alkalinity goes down and vice versa. They sort of occupy the same chemical “real estate” in seawater. Here’s a simple way to understand the balance.

Imagine  a jar full of blue and white marbles. White marbles are calcium and blue marbles are alkalinity. Every second of every day your tank is pulling out one blue and one white marble. Eventually, the jar starts to empty. If you use a calcium supplement, you are adding more white marbles and no blue marbles, so the jar now becomes imbalanced.  But something else happens. As you add the white marbles, some of the remaining blue marbles fly out of the jar all by themselves (precipitation). Likewise, if you add alkalinity buffers to your tank, some of the white marbles would jump out of the jar. The more you dose, the worse it gets. For this reason, it is almost impossible to maintain balanced calcium/alkalinity levels in your tank using separate additives like “liquid calcium” and alkalinity buffers or baking soda.

Even if you have high calcium levels say, 500ppm your corals can’t use any of it if alkalinity is low.

Everything in your tank uses calcium/alkalinity (calcium carbonate) in balance. It doesn’t matter if it’s being consumed by coralline algae, growing snails, growing SPS/LPS, or white deposits on your heater and water pumps. it is all one part calcium and one part carbon.

First Steps

Before dosing any two part additive, you need to determine the calcium/alkalinity levels for your tank. The best way to do this is to measure a newly mixed batch of seawater. The calcium and alkalinity readings will become your target. If you’re not satisfied with the numbers, use a different salt mix or raise your salinity. I have seen spectacular reef tanks using plain old Instant Ocean, so don’t get too hung up on the actual values.

If you’ve been using separate calcium and alkalinity buffers, your tank is probably out of whack. Perform a large water change to get things back in balance. If you haven’t used separate additives but your tank readings are a little lower or higher than your seawater mix, don’t worry about. If there are large differences, then a hefty water change is a great way to start.

Initial Dosing

The amount of two part additive to use will be different for every tank. I suggest an initial dose of 15ml of each part per 25 gallons per day. It is best to dose in the morning when the pH is lowest. It’s important that the two components do not come in contact with one another or it will turn into a gooey white mess and become useless. I usually dose the alkalinity component directly into my overflow and down the sump and dose the calcium component into the tank in front of a powerhead. You can also stagger the dosing so that you dose one, wait 5 minutes, then dose the other.

Real Life Scenario

I recently setup another reef tank and will walk you through on how to use 2 part additives as well as determining how much to use.

  1.  My freshly mixed seawater has a calcium reading of 420ppm and an alkalinity reading of 3.2 meq/l (8.9 dKH). The tank was reading 430ppm and 3.05 meq/l (8.5 dKH). It was different, but close enough.
  2. I started with 15ml per 25 gallons of each component, dosed every morning.
  3. You need to wait at least a week before taking a reading. Don’t take a reading right after dosing. Wait at least several hours. I dose in the morning and when need be, take readings in the late afternoon.
  4. After waiting a week, I took my first readings. My calcium level was 510 ppm and my alkalinity was 2.9 meq/l (8.1 dKH).
  5. Yikes! The first reaction from most aquarists is that I need to add alkalinity buffers. In fact, you don’t need alkalinity buffers, you need more two-part. At this point, I raised the dosage to 20ml each per 25 gallons.
  6. After dosing for a week, new readings revealed that calcium was 450 ppm and alkalinity was reading 3.0 meq/l (8.4 dKH). Not quite there yet.
  7. I raised the dosage to just shy of 25 ml per day.
  8. A week later, I read 440ppm and 3.15 meq/l (8.8 dKH). This was close enough. Future water changes will slowly adjust the levels even closer.

Facts To Remember

  • Never dose unequal parts of the two components. There is no reason to ever do this as both parts are always consumed equally and converted into calcium carbonate and nothing else. If you try it, you will just knock your tank out of balance again.
  • Don’t use separately sold calcium and alkalinity products. I’ve been keeping marine tanks for 30 years and I have never been able to achieve ionic balance when using these products.
  • You don’t need to measure calcium levels. Once you calcium/alkalinity is balanced, just measuring alkalinity will suffice.
  • Measure your alkalinity at least once a month. If you have lots of livestock that is actively growing or you add more livestock, you might need to make adjustments to your dosing amounts as time goes on.
  • Be aware that some additives that have nothing to do with calcium/alkalinity control may actually contain calcium and/or alkalinity buffers. Overuse of these products can interfere with your 2-part dosing.
  • Most people don’t use enough 2-part and wind up with very low alkalinity levels. Similarly, overdosing 2-part will result in alkalinity levels rising higher than your salt mix measurements. Take it slow- It’s pretty easy to find the right dose for your tank but give it at least a week between readings before making any adjustments.
  • For large reef tanks, 2-part additives can get expensive. In the long running a calcium reactor will cost less.
  • There are many brands of 2-part additives including the do it yourself chemicals. Some of the best brands are B-ionic, TLF C-Balance, Brightwell ReefCode-A and Reef-Code-B, Seachem Reef Fusion 1 and 2, and Kent Tech CB Part A and B. These premium brands also contain other needed supplements such as trace elements and magnesium. It doesn’t hurt to try a different brand once in a while to see what works best for your tank. Based on my testing here is how I rate the brands I have tried:
1 ESV B-Ionic The original is still the best. 2-part plus trace elements and magnesium all in one.
2 Brightwell Reef Code A B Strong formula. Use less than other brands.
3 Seachem Reef Fusion 1 and 2 Components dissolves quickly, medium-strong formula. A bit pricey.
4 TLF C-Balance General purpose formula. Has magnesium and strontium but not at high enough concentrations to make a difference.
5 Kent CB Part A B Less expensive than others. It worked to maintain Ca/Alk, but for me livestock didn’t “pop” like other brands. As always YMMV.
6 DIY Economical, but weak. Needs to be supplemented with trace elements, strontium, magnesium. Questionable purity (DIY use of sidewalk de-icers for calcium component).

 Making It Easy

Anything that needs to be done once a day needs to be easy to do. I’ve tried dosing with measuring cups, shot glasses, and syringes. It’s just too much work measuring out each part, especially for nano tanks.



Beddix Bottle

Beddix Bottle

I found an excellent dosing bottle called a Measure-Matic lab dispensing bottle. They are a bit expensive, but very easy to use. You don’t need to measure anything. Just set the top cap level and then give a squeeze. Any excess automatically drains back into the bottle. These are excellent for small tanks where you need to dose up to 25ml.

For larger tanks, or if you need to dose >25ml, you can use a Beddix bottle. You’ve probably used these before as they are common for garden chemicals and pesticides. It works similar to the Measure-Matic but you need to squeeze out the amount you need. The numbers are a little hard to read, but you can fix that by going over the plastic embossed numbers with a magic marker.

‘Till next time – Joe

Note that links in this article will take you to Amazon where you may purchase these products. I receive a small commission from Amazon (not paid by you) to help defray the costs associated with this blog. Thanks for your support!


  1. thanks for all your inf.about reef tanks.

  2. I’ve done what u said. Waited a week and my calcium is at 320 but my alk is at 8.6 do I do more 2 part or less?

    • Please wait another week before adjusting the dosage. These levels won’t harm your livestock. It sometimes takes a little longer to stabilize Ca/Alk.

      If after a week from now alkalinity continues to rise, then reduce dosing by about 20%. Wait 2 weeks and test again. If alkalinity is not rising anymore and is stable or dropping, keep dosing the same amount. You should see calcium levels start to rise.

  3. I sure can use your help as I can never get this right. So I have esv 2 part. With a 100g and 20g sump. So u are saying 15ml per 25g of each cal and alk?= So I should be dosing 60ml a day of both cal and alk? I’ve been chasing one or the other for weeks dosing one or the other. So if I keep dosing this amount everyday It will eventually balance out?

    • All 2-part additives need to be dosed in equal portions. I would guess your tank now a bit out of whack if you were dosing unequally. Do a large water change to get the tank water back in balance.

      15ml per 25 gal (100L) per day is a starting point. So yes, for a 100 gallon tank you will need 60mL of each part dosed once per day. For a tank your size, it would be less expensive in the long run to install a calcium reactor.

      • so he keeps dosing and testing everyday until he reaches balance?

  4. No, never test daily. It takes at least 1-2 weeks for the Ca/Alk to stabilize where you can get a good reading. So dose daily, but test twice a month.

  5. I have Instant Ocean Reef Crystals that says it has Calcium Magnesium and extra trace elements do I still need to use separate additives?

    • Regardless of salt brand, marine tanks generally use more calcium/carbonates than can be replenished by water changes. Measure the alkalinity in a newly mixed batch of seawater and the alkalinity in your tank. If your tank is lower, you need supplementation.

      • At the moment I dose weekly and do water changes twice a week. It keeps the measures in check and my tank is thriving. (about to upgrade) need a tank thats drilled, and also I am going to get a pan for under the stand so that water doesn’t get on our wood floors.

  6. How does Mg interact n this equation please? Doesn’t it act as a stablizer for alk and cal?

    • As long as Magnesium levels are in the natural seawater range (1300 ppm +/- 200 ppm) It will not cause calcium precipitation.

  7. Everyone keeps saying to use equal amounts of both parts, but that is meaningless if the amount of powder I can dissolve in RO is different for each part. I use a doser set to 10 daily doses. Dosing 160 ml of alk but 27 ml of calcium. I can dissolve a lot more calcium in the RO. Do you think I should make a weak solution of calcium so that I can make them equal? I’m using Seachem builder, and advantage calcium. I’m considering switching to Redsea two part with the three bottles. PH never moves off of 8.3.

    • As I mentioned in the article, you’re using separate Calcium and Alkalinity powders which is very difficult if not impossible to achieve balance. 2-part additives come in the proper Ca/Alk ratio so you don’t have to screw around with these products.

  8. am confused how does it work to balance cal/alk. the example says, he started with initial dose of 15ml which gives him result of 520 cal and 8.1 alk. so he raised the dosing from 15 ml to 25 ml. am expecting both cal and alk will increase but then cal went down to 450 and alk raised to 8.4. with my situation: am dosing 15 ml of cal and alk everyday for 2 months now (65 gal tank) and am getting 12.6 alk and and 470 cal. i think perfect numbers to grow corals but then am getting RTN to my sps. so am thinking to reduce both cal and alk. i started to reduce the dosing yesterday from 15ml to 14ml (that’s less 1ml) both cal and alk. i tested this morning and from 12.6, alk went down to 12.3. However, my calcium went down from 470 to 270 (i hope, i was just wrong). any idea if should i reduce or increase my dosage? or should i just give up?

  9. am confused how does it work to balance cal/alk. the example says, he started with initial dose of 15ml which gives him result of 520 cal and 8.1 alk. so he raised the dosing from 15 ml to 25 ml. am expecting both cal and alk will increase but then cal went down to 450 and alk raised to 8.4. with my situation: am dosing 15 ml of cal and alk everyday for 2 months now (65 gal tank) and am getting 12.6 alk and and 470 cal. i think perfect numbers to grow corals but then am getting RTN to my sps. so am thinking to reduce both cal and alk. i started to reduce the dosing yesterday from 15ml to 14ml (that’s less 1ml) both cal and alk. i tested this morning and from 12.6, alk went down to 12.3. However, my calcium went down from 470 to 270 (i hope, i was just wrong). any idea if should i reduce or increase my dosage? or should i just give up? lol

    • I don’t believe your RTN issue has anything to do with Ca/Alk levels.

      In any case, your levels seem to be on the high side (470ppm & 12.6 dKH). You could reduce 2-part additive dosage by 30% and then after 2 weeks test to see where you’re at. Or just leave it alone. There no reason to chase numbers because someone on a reef forum said they need to be this or that to grow corals.

      Also, an alkalinity drop from 12.6 to 12.3 is reasonable, but I think you need to retest calcium. Going from 470ppm to 270ppm in one day seems unlikely, probably bad test results.

      • if am going to reduce my 2 part doe by 30%, then i will end up about 10ml of calc/alk per day which i think is very low amount for 65 gal tank (mixed reef). whereas, the suggested initial dosing is 15 ml per 25 gal. so, for 60 gal, i am supposedly dosing 30ml per day. what if i raise my dosing instead from 15 ml to 30 ml (increase 5 ml per day), i wonder if my calc and alkaline will be on point.

  10. Joe my salt mix is low on alk. 6.2. so after mixing a batch I usually add a small dose of part 2 to raise it. Is this a bad idea. should I change to a different brand? Thanks

    • Brian, As long as your pH is between 7.8 and 8.5 I wouldn’t worry about it.

  11. Quick question. I’m doing a two part via Apex DOS. It’s a 225 mixed reef. I’m up to 90ml/day of both calc and all dosing evenly. My calc and all were coming down evenly then split and ALK started riding while calc didn’t. Does that mean I’m now over dosing and need to pull back? I’d post a screen shot of my Apex but there site won’t let me. Thank you.

    • Yes, sounds like you are overdosing 2-part. Cut back 10-20ml daily.

      • Ok. Two weeks ago I dropped my calc/all dose 20ml/day. The first week it looked like it was correcting(calc went up from 425 to 435, all came down from 8.3 to 8). Today at the two week mark my calc tanked down to 416 and alk remained 8.1. Do I reduce my dosing more?

      • I’ve reduced my dosing by 20ml/day. After the first week it looked like it was correcting. Alk dropped from 8.3 to 8 and calc rose from 425 to 435. Today was the two week mark and alk is at 8.1 and calc at 416. Calc got worse. Should I reduce dose more?

      • Your readings are fine and I wouldn’t worry about. 425ppm vs 435ppm Ca is stable. A 10 ppm difference is easily within the accuracy of the test kit. Likewise, pH will fluctuate quite a bit within a 24hr period.

  12. I recently checked my levels and notices they were sub 290 calc (test kit doesn’t go lower) and 12 alk.

    I have a 60g tank and was dosing equal parts 24 ml /day.

    I assume I can’t correct this without a water change first but how large of a water change should I do?


    • High Alk and very low Ca is a common issue for tanks that have, at one point, been dosed with Alk buffers, baking soda, or pH adjusting powders. A large water change (close to 50%) will help a lot. Then, subsequent routine water changes over time will get the tank back in balance. I wouldn’t start dosing 2-part for at least 2 weeks after the large water change. Check Ca/Alk a week later, then again after another week. if both Ca and Alk are falling consistently then start your 2-part dosing at initially low levels.

      • Thanks for the advice. So after 1 week and a 50% water change my readings were: Calc:325 / Alk:6, and after 2 weeks they were Calc:335 / alk 5.5. Should I start dosing now or wait longer? The numbers seem to have not really moved after the first week.
        (P.S. you were absolutely right about the previous use of buffers in my tank.)

      • Yes, start dosing now. You will see both Ca and Alk Rising. Give it some time and don’t panic if you first see Ca jumping high off the charts with Alk still falling. if this happens increase 2-part dosing by 25-50% and give it several weeks to settle down.

        Important thing is don’t try to chase numbers or shoot for some exact numbers. When Ca/Alk levels are within normal parameters (Ca 390 to 440 mg/l, Alk 2.8 – 4.5 meq/l) you found the right daily dose and stick with it.

  13. is it ok to dose ca during the day and alk during the night.
    im dosing ca from 9am to 9pm 15ml then at 10:30 pm alk until 8am at 15 ml

    • I suppose that would work, but don’t understand why you want it to it that way.

      • How should I do it, that’s what I’m asking, how should it be please tell me

  14. so what is a better way

    • The method I describe here is very simple and easy- Just add the daily dose in the morning of both Alk and Ca in different parts of the tank. In my opinion, drip dosing using a dosing pump is not necessary. Your corals will use what they need regardless of present levels. So dumping the daily amount all at once works fine.
      – Joe

  15. what recommendations would you have for a 12 gallon nano. I currently have 9 sps corals in my tank. i use red sea coral pro and i do weekly water changes.

    • You may not need any 2-part. Check you Ca and Alk levels before your weekly water changes and if they are close to your salt mix, then it’s not necessary.

      • So, when is it a good time to do a water change?

      • The weekly water changes you are doing are fine. It doesn’t matter what time of day you do it.
        – Joe

      • I have another question… how come my ph goes from 8 during lights out to 8.48 until lights out

      • The biggest factor affecting pH values in aquariums is carbon dioxide accumulation. During the day, photosynthesis absorbs CO2 from the water and the pH rises. During the night, the pH falls as dissolved CO2 in the water rises.

      • Okay I just tested my tank water and its alk- 6.72/ cal- 350. I also tested my new saltwater mix from red sea salt. Alk-12.3/ cal- 455. What do you recommend?

  16. Hi, I established my tank 9 moths ago. Until now, it was fish only. Now, I am planing to add some corals. I start checking my parameters and found out that I have very very high level of calcium, 700ppm while Alkalinity is 8.1dKH (I repeated calcium test many times, it is true). An employee in local store told me this would be the result of the salt that I am using, which is D-D H2Ocean. Now I have ESV two part dosing solutions, but not started dosing yet. You suggested that never dose unbalanced amounts but when calcium is this much high, dosing more calcium really scares me. I don’t wanna make any mistakes. Please help me to start dosing. I have 50g tank. Thanks!

    • I don’t think your levels are a result of the salt mix brand (H2O Ocean quotes 440 ppm Ca and 9.3 dKH on the product labeling). You can Either do a large water change to re-balance or just wait for the levels to fall naturally.

      • I did large (15%-20%) water changes couple of times w/o any decline in Ca. The local store staff claimed that sometimes salt mixed can be not homogeneously mixed because of production or transportation. He said the rest of the salt that I have might include higher Ca level. I ran a Ca test for NSW, which was showing 600ppm… So in this case what you are suggesting is do not start dosing, just wait? Again people in the local store told me to start dosing only Alk first, then eventually Ca would decrease so I could start dosing Ca as well. What do you think about this statement? Thanks!

      • If you are saying you did a calcium test on natural seawater and found levels to be 600 mg/l, then there is something wrong with your test kit. Natural seawater calcium concentration ranges from 380 – 420 mg/l worldwide. I would try another test kit before doing anything else.

  17. I’m still having a little trouble with this. My levels seem to be moving in ways that you are not addressing. I’ve been dosing my 225 at 60ml per day of two part. Last week I had 440ppm and 8.4dkh. This will I have 435 and 7.9dkh. I don’t do regular water changes as I use an AT scrubber and supplement trace elements. I did add some extra calc two weeks ago because my Alk was down to 410ppm. I know my numbers are ok but I’d like to get more in depth in scenarios. such as what to do when both levels are falling. I’ve brought my levels up before just to get faster drop in calc and rise in Alk. I think I’m pretty close now but could use some discussion for your opinions on a few other points with my system. If you are willing to talk over the phone send me a good contact number. Thanks.

    • “I did add some extra calc two weeks ago” – use of separate calcium and alkalinity buffers is what this article is all about. By using a balanced 2-part additive, you avoid this “chasing of numbers”. I suspect your tank is doing fine regardless of varying calcium/alkalinity readings.

      If both numbers are low or one is low and the other is very high, increase your 2-part dose slightly and test again in a few weeks or months. Most people test too frequently and wind up under/over dosing- it takes time for these additives to stabilize.

      You said that you do not do regular water changes. Perhaps your tank is out of balance to begin with because of previous calcium and alkalinity additives.

      • The tank is doing great! But I’d like to see a like faster Coral growth. The tank has always been fairly within limits. It’s been running for 4 years and I bought and moved it to my house in March. It was our of balance when I got it and did do some water changes to correct that. Once I got the levels close I bought an Apex DÖS system and had been making small adjustments since. I’m dosing 60ml of each constantly. 12hrs of ALK at night and 12hrs of calc during the day. I test water every Sunday afternoon. I’ll try to up my dosage a little and see what happens. I’d still like to chat and have a way to send you a trend graph of the parameters from my Apex. FYI I’m using BRS two part with their Mag mix. Also is it better to have the DÖS dose one time each per day or continue with the small continuing dosing through there day?

  18. Excellent and straight to the point Joe! Thanks, you have been helpful for me over the past 5 years or so. Joe, do you acclimate your corals, like fish?

    • I do acclimate corals similar to fish, but much faster:
      (1) equalize temperature (float bag in tank) maybe 5 min.
      (2) Add tank water twice at 5 min intervals to equal water volume of bag.
      (3) Do a quick iodine dip.
      (4) Release.

      • Thanks so very much. Greatly appreciated.

  19. Joe,
    I am dosing 200 ml per day of each solution. I use BRS two part. Does this seem like a lot? I have a 75 gallon reef. Stock is SPS and LPS. Levels hover around 8.5 dkh and 420 calcium. Just worried that I am overdosing. I’ve read people info that have much bigger tanks that dose much less than I do. Any info would be appreciated. PS I do not notice much precipitation and my magnesium is 1430.

    • I’ve never used the BRS product so I don’t know its concentration. I would try reducing your dosing by 50% (100 ml a day). Test after a week and see if there is a significant drop in Alk/Ca.

      • Just a follow up to the post above. I have cut the dosing in half. I did test this morning and dkh is at 7.2 and ca is at 410. Should I continue to ride the lower dosage out? Just worried of levels dropping too far.

        Thanks in advance

      • 100 ml/day is more in line with a 75G tank. I would continue at this rate and measure weekly to spot check levels. And don’t worry about lower levels- A lot of people try and push Alk/Ca/Mg to their limits and then find out it made no difference to their livestock.

      • Joe question for you. The other day i did a major over haul on my aquascape and really cleaned my substrate. The next day my Alk went up to 9.5 which I am happy about. Calcium is at 420. Would cleaning make the levels change that much. I was at about 8.2dkh before the cleaning.

      • Alkalinity cannot rise on its own. There is no biological activity that can raise Alkalinity. I suspect that the replacement seawater you used after the cleaning process is the cause. If you use tap water for top off, that can also raise alkalinity.

      • Thanks Joe. I’ve always used the same salt mix. Red Sea reef pro. Also have usually changed about the same amount of water without raising levels that much. I did remove some rock. I dose 130ml 2 part per day I. My 75 gallon mixed reef. Also use rodi water for top off.

  20. Thanks for the article. In your “Real life scenario” example, what was the net aquarium water volume of the tank? Also is there an online reef calculator you recommend?


    • The real life scenario was done on a 40 gallon tank.
      As for the reef calculator, there as some that determine how much calcium and buffer are needed to bring a tank to certain levels, but 2-part dosing is all about daily replenishment with each aquarium requiring different amounts.

      • Ahhh, LIGHT BULB!!!…after reading so many online articles about 2-part dosing that were confusing and too technical, your’s was the best and easiest to understand that explained where the target #’s were coming from. Wish others had mentioned about taking measurement of freshly made saltwater to recognize your own tank’s specific dosing need. Now it all makes sense, THANKS Joe!

        do you recommend starting out with 15ml per 25 gallons of each component when first starting to dose no matter what tank size?


      • Yes, 10-15 ml per 25 gallons is a good starting point no matter what the volume.

  21. what if I’m currently using Kalkwasser, should I use less than 10-15 ml per 25 gallons?

    • You may be able to use less. The only way to know is to measure Calcium and Alkalinity levels over time.

      • Joe, read your article and have been following the replies. Great stuff. I have a 120 gal tank. Did a 30 gal water change a week ago and did some measurements today (1/28). Salinity=1.025, Nitrate=0.2, dKH=~9.0, Alk=~3.25, Calcium is 475. I’ve been dosing 90ml of ESV 2 part. Should I continue at 90ml or make a change? I believe the numbers are in the ballpark. Thanks.

      • If your tank is doing well, I wouldn’t change anything. If you want you can experiment with less 2-part by reducing dosage 25% for a month or so and see if there are any negative effects.

  22. “If your tank is doing well” – that’s the million dollar question. Fish are all good. I’m more concerned that all is well with the water when it comes to the corals. I had some mushrooms the looked fine for about a week and then just shriveled up and died. Now I’m a bit concerned about my Elegance Coral. Looked great for about a week and now doesn’t seem to be opening up fully. I also have an Acan coral that’s sort of showing signs of not being too healthy in the last day. The Elegance and Acan were both added with the last 2 weeks. The mushrooms were added about 2 weeks prior to that (4 weeks ago) and were done and gone before I added the others. I have other corals and zonanthids that appear to be doing fine. Thoughts?

    • An Alk/Calcium imbalance is unlikely to cause these livestock health problems so rapidly. It’s hard to tell what exact problems exists without seeing the tank and its parameters. Some general things you can try is a large water change (in the event that a toxin or excess pollution is the problem), Feeding your corals (all that you mentioned can feed on mysis or finely chopped food), or perhaps a deficiency of iodide (dose 1 drop per 20 gallons of Lugol’s Solution). Again, these are a stabs in the dark and just general things to try.

      If you belong to a Reef club or know someone with more experience, it’s a great way to learn and to solve problems quickly.

      • Thanks Joe. I appreciate the help.

  23. Hi Joe, I was adding 12.5 Alk and 25 Cal two part dosing and then my tank had low ALK so I upped the ALK to 17 and now my Caps and some montis are turning white.. My latest readings are alk 8.5 and my Cal 475.. whats going on – how to adjust ?

    • The premise of the article is that 2-part additives should never be dosed in unequal proportions. You will need to correct your situation with large water changes.

      • Yes, going forward I will try this method.. but with the right pars currently why would the bleaching be happening ?

      • Ca/Alk imbalance is most likely not the cause of your coral bleaching.

  24. Hi Joe, I have a 125g mix reef tank with a 30g sump/refugium and a 20g long fraq tank plumbed into the main system. The main tank has been set up for 2 years and the fraq tank was added about a month and a half ago. I have been dosing 105ml (15ml/25g) per day of both parts of Ocean’s Blend. The Ca is 450 and the Alk is 8.1 dkh. all the corals seem to be doing great with good growth. Should I increase the two part to 20ml/25g or does the current parameters look good to you?

    • Nick,
      Those numbers look fine. If Calcium ever rises to close to 500, then I would try increasing 2-part dosing amounts. But for now, you’re looking good.


      • Thanks Joe, I just wanted to make sure.

  25. I’m new to dosing, so I hope you can help me out with 2 part so when dosing calcium how long do you dose for do you dose for 8 hours every hour or three times in one day I’m really not sure I have a 90 gallon saltwater tank so I need some help on how much do I dose a day is it like 15 milliliters every hour please help me out thank you

    • This article explains daily, manual dosing of a 2-part additive in an aquarium. Please read the article again – This is about daily dosing (once a day) and how do determine how much to dose via water testing over time.

  26. Thanks for all of your help.
    My calcium is a 400 so should I dose more cal 10ml over the next 2 weeks or should I dose more like 15ml over 3 weeks or is it good were it is.?

    • Use a test kit to measure calcium + alkalinity. Wait 2 weeks, then do another water test. If calcium is rising, increase 2-part. If it’s falling or steady (+/- 10%) then don’t change anything.

      • Thanks Joe, for your help let you know how things are going in about 2 weeks or so and again thanks for your help.

      • Joe,I have a 90 gallon tank how much 2 part should I be dosing. Should I start out at 15ml. Or should I doses 60ml I don’t won’t to over dose my tank. Now my cal is 400 alk is 7.9 this is after a water change. What should I do 15ml or 60ml I’m really not sure.
        Thanks for your help.

  27. Hi Joe
    Just want to start of by saying what a great article you have wrote, very good way of explaining the two part dosing.
    I have been dosing two part for about 6 months now and Im still trying to get my calcium levels down to around 450. Right now they are at 500+ and alk is around 8.0. I am dosing 72 ml of a and b each day on my 90 gallon tank. From what i have read on your article it seem like I need to up my dosage just a bit more to get the levels just right. Is this correct? My tank is pretty heavy stocked with sps.

    Thanks again for the great write up. I keep coming back to it for more advise.

    • Greg, it does sound like you’re underdosing, I have a 24 gallon nano reef mostly SPS’s where I dose 25 ml of each part daily. I would try boosting to maybe 100 ml each part daily for 3 weeks then take another reading to see where you’re at. If you see calcium drop then maybe back off by 5-10 ml every few weeks to find the sweet spot. Don’t go overboard on chasing numbers- demand for Ca/Alk does vary so it will never be super stable at some values.

      • Thank you for the reply. I’ll try that and post what happens

      • So I just tested my waters. Dkh is at 9.8 and calcium is at 575. It’s only been about a week since I’ve started dosing more so I will continue dosing the way I am and test again next week to see how things change.

  28. Joe I have a question. I use reef pro from red see. I dose esv for calcium and alkalinity. I am currently dosing 70 ml of each per day. After a water change of ten gallon on a 75 cube mixed reefI notice that the levels drop. I don’t know why this happens. The mixed batch of salt water has higher values. Then I notice after about a week my levels start to climb. Currently at 8.7 and 430 magnesium 1420. Why would this happen. Thanks in advance. Doug

    • What may be happening is there is a brief Ca/Alk imbalance when the two waters are mixed, and it takes some time for equilibrium to come back. I wouldn’t worry about.

  29. Joe,
    Have a newer Red Sea Reefer 250. I am dosing 15ml per day Two Part Bionic with an Apex D.O.S. My alk is 9.5 and Calcium 440. In reading your article and posts above it looks like I am under dosing. Tank Size is 55 Gallon… Should I be doing 30ml per day of each part???

    • Steven,
      You Ca/Alk levels look fine (just a little on the high side). I would leave things as they are. The dosage per gallon is just a starting point as all tanks are different.

  30. Hi Joe,

    Is it safe to dose two-part the same day I do a water change? I’ve been reefing for almost 30 years and have long done SPS, but I’m moving into a lot more Acros and decided to start dosing two-part. I’m using Kent Reef Salt because the numbers are good right from the mix so I followed with Kent’s two-part called Kent TechCB. My first dose was a week ago today and I waited a week before testing my numbers and they’re great. Alk is 9.7, Calc is 420, and Mag’s at 1470, which is a little high but within the +/- range you recommend. I’d appreciate your take on dosing the same day as a water change. It’s only 10 gallons because I do 10G once per week on a total volume of a little under 100 gallons so I don’t think it’d be a problem. Would appreciate your take. Thanks so much.

    • Hi Peggy,

      Perfectly fine to dose two part on the day of a water change. Preferably, do the dosing AFTER the water change.
      – Joe

  31. Hi Joe,

    Peggy here. I’ve been dosing daily as I mentioned in my initial inquiry and my dKH seems to be riding high at 11.2. Mag is still a bit high but within the range you suggest. I have a couple Acros that appear to be stressed so I’m wondering what the best method is to bring down my dKH. I skipped my water change this week thinking perhaps the Alk would drop off and it did a little but not significantly. Other Acros are doing well so it could be my eight-lamp T5 is a bit much for the problem children but I stagger the lamp times and don’t run all eight for the full lighting schedule. All Montipora are growing like weeds and the Tridacna derasa has grown considerably in the short time I’ve had him. All other SPS are thriving. I know there are conflicting opinions about best Alk levels for SPS and it makes my head hurt to read most of them. I used to run an SPS and clam system where I never dosed and all was well. I’m tempted to return to those simple practices. Any suggestions to lower my dKH would be appreciated. I’d like to run around 9 and am also considering dropping my sg to 1.025 from 1.026 simply because the Kent Reef Salt has high numbers on all parameters upon mix. Look forward to your reply.

    • Difficult to tell what’s causing your acro to be stressed. If it is a Ca/Alk/Mg issue, I would suspect Mg being too high. But again, it could be a variety of things whenever some SPS’s are doing well and others are not.

      As long as Ca/Alk is balanced, simply stop dosing 2-part should cause Alk levels to fall. If not, there is some other source of carbonates entering the tank. Perhaps top-off water or water used in salt mixing, also additives for other purposes can contain carbonates.

      By all means, experiment. Your previously successful Clam/SPS tank without any additives did well- you can certainly try that again.

      • Hi Joe. Thanks for your prompt response. I believe it’s a high Mag and Alk issue. I tested everything yesterday again and Alk is still 11.2 and Mag is 1470, the latter of which still does fall within your +/- 200 range, but I’m going to stop dosing and check each day to see what my numbers are. There’s no carbonate issue. I use RO/DI only and don’t use any buffers or anything so I’ll just follow the numbers for a bit and see where it goes. I’m sure it’ll all fall into place. Thanks again for your time. I appreciate it.

  32. Hi Joe,
    I have been reading your comments and they were really good. My question is the dosing interval. I used to do 12midnight to 6am for alkalinity and calcium from 6am to 12 pm and have my Automatic Water Change from 12 noon to midnight using Apex DOS.

    Would it make it better if I dose the Alkalinity and calcium every other hour alternately rather than 12-6am and 6am to 12 noon? The reason being is that when I checked the Alkalinity early in the morning around 8:00 am, the Alkalinity was 14 and my calcium was at 380. Of course the Alkalinity just finished it’s dosing and Calcium just started and have more ways to go until 12 noon and I am sure it will both balance out in the late afternoon. When I used to check it late afternoon, Alkalinity is at 11 and calcium is 440. Am I right?

    • Just about any scheme will work. I dose manually once a day and have been doing it this way for years with no problems.

  33. Hi Joe,
    It’s me Rick again. Do you deduct the weight of the live rock from the toal weight of the water when you are calculating the dosing? Thanks

    • It wouldn’t be weight of live rock but volume that displaces water. In any case, way too complicated to mess with. Just find the right dose with trial and error and don’t test within a few hours of dosing.

      • That makes sense; Trial and error, as there are too many variables such as how much corals or what kind I have.

  34. Hi Joe,
    I thankyou for such simple and easy to follow suggestions . . . I am just about to dose using a quality dosing pump system. This allows me to set the total amount to be dosed per day and dial in the frequency per day of dosing . . . It then determines the amount it will dose each time. I can select from once to 24 times per day and set when to dose ie over the 24 hour period. My gut feeling is to dose 24 times over the whole day period . . . Can you comment on this gut feeling and/or offer an alternative. Thanks again and in anticipation of your sage advice.

    • Once per hour dosing of the total day’s amount would be fine.

  35. Hi Again Joe,
    If I can squeeze you for another question . . . I notice this Blog refers only to mixed salt water. In Australia, we are blessed with vast expanses of beaches with very little pollution etc and most reefers around Adelaide use natural sea water or water that has been sanitised and cleaned by processing organisations for the aquaculture industry. I am just wondering if any of your dosing information or recommendations would need to be adjusted if we use natural or sanitised sea water.

    • Tony, natural sea water is a bit more stable than mixed. You might get away with using less 2-part. Use same instructions though to measure the NSW Calcium/Alkalinity and then go from there.

  36. HI Joe,
    Found this article 2 weeks ago and got my tank in balance with a large water change. I started dosing 10 ml of each for a week and just took my first test..Calcium is 475ppm and Alk is 12.5 dkh. My tank is a 20 gallon with mostly lps and a few sps. Should I continue the 10ml or cut back?

    • Both parameters are little high. Calcium should be kept below 450. I would reduce dosage to perhaps 7 mL each day and go from there.

      • Thank you for your help and fast response!!

  37. Hi Joe,

    Your post inspired me to start 2 part dosing, before I did my monthly water change on my 45g tall with a 30g long sump (I would say 65g total volume). I tested my tank, due note that I do use kalk in my ATO.

    Ph at end of day 8.3
    KH – 8
    Cal- 360
    Mag – 1140(probably due to kalk dosing)

    it has only been 4 days since I started dosing 2 part of 40ml each per day, I’m also adding 250ml of mag to raise my levels to the proper levels, I already dosed 1000ml of mag and still have about 100ml to go. I was curious what my levels are so I tested my tank today.

    PH – 8.64
    KH – 11
    Cal – 500
    Mag – I’m testing tomorrow to see if it’s 1350 after 1100ml of dosing

    I’m a little scared of the numbers but all my corals and fish are fine. Should I continue 40ml of each per day until I hit the 2 week mark or should I dramatically cut the dosing to like half (20ml of each). Since my PH is so high maybe I should stop using kalk or a lower concentration of kalk.

    Thank you for any advise you can give.

    • Hey Jim,

      All those readings are quite a bit higher than NSW. I’m most concerned about pH which at that level can be detrimental to your livestock and/or cause excessive calcium deposits on heaters, pumps, etc.

      Your original readings prior to using 2-part look fine. The combination of water changes, limewater dosing, and nominal calcium demand makes your setup marginal in the need of a 2-part additive. My recommendation is to not use it at all. But if you want to push your Ca/Alk up a little, start with 10ml a day and test after a week or two to see where you’re at.

      • Thanks for the reply, I have been told that I don’t need 2 part but the thing is since I been added more sps lately, absolutely nothing grows anymore sps, lps, etc… lets put it this way I have a sunset monti for almost 2 years now it has only grown to maybe 10% the original size since I bought it.

      • Jim, a lot of things can cause slow growth and it’s hard to pinpoint the exact problem. In my experience, more frequent sps feedings has had the greatest effect.

      • Oh man chasing numbers is giving me a headache, before I left for work this morning I dosed 100ml of Mag to finish up the 1100ml to boost my mag to 1350 levels. I tested the mag when I got home (at least 9-10 hours have passed) it’s at 1380 that’s good enough for me.

        I decided to test my PH again and this was before the lights were on and I got 8.4#(something) on my PH pen, I decided to try the api high range (expired) and I got 8.2 so I re-calibrated my PH pen and got 8.41. Then I used a High range api that is not expired and got the same 8.2. I know that I forgot to turn on my ato after feeding last night so that might explain the lower PH and that my lights were not on yet, I’m going to test it with the Pen again before my lights turn off tonight.

        I also tested my KH, api – 10, Sailfert 10.6

        Here is where I’m frustrated, using api’s calcium test I got 460ppm, using sailfert test I got 375pm….. I did the sailfert test again and got the same 375ppm. That’s a huge difference in reading I don’t know what to believe both kits are not expired.

        I have not dose cal or alk today.

  38. Can you talk about when to dose bionic magnesium? And what effects that has on alk and calcium when not used or overdosed?

    • Mg should not be dosed unless tested. 1250 – 1350 mg/l should be maintained. Overdosing will cause abiotic calcium carbonate precipitation (on equipment and surfaces). Very low Mg levels (<800 mg/l) will wreak havoc with pH/alkalinity.

      Many tanks do not need Mg adjustment. Any tank that gets frequent water changes and has low amounts of coralline algae (i.e. tanks with bright lighting) will not use much. Many salt mixes (such as Instant Ocean varieties) have elevated Mg levels to begin with. Again, measure before dosing. And don't raise Mg faster than 100 mg/l per 24 hours.

  39. i know many people with successful flourishing tanks that dont do water changes.

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