The Carbonates Controversy in Aquaponics

carbonates in aquaponicsLast May I wrote a post titled “pH and Water Hardness in Your Aquaponics System”. In that post, I explored the relationship between pH movement, alkalinity and KH or carbonate hardness.  Since then, there has been some swirling controversy about the use of carbonates in aquaponics.  In this post, I hope to end the controversy by explaining why we use carbonates in all of our systems and why you should as well.

To review, carbonates “buffer” or modulate the movement of pH in your water.  Buffer strength indicates how well the water in a system resists pH change when either an acid or a base is added.  You can measure buffer strength using an API GH and KH test kit, and strengthen your buffer by adding potassium bi-carbonate (our new AquaBuffer product).  The general Rule of Thumb in the aquarium industry is that you should have carbonate levels of at least 4 dKH (dissolved carbonate hardness) or measured another way, 18 parts per million (ppm) of carbonates.

Why would you want to create a buffer in your aquaponics system?  There are a few critical reasons.  First, while fish can generally adapt to pH levels that are outside of their ideal range, they cannot handle dramatic, rapid swings in pH.  At The Aquaponic Source, we take phone calls every week from customers who are struggling with what appear to be random fish deaths.  When we ask them to measure their pH several times during the day, we often see dangerous intra-day swings of an entire point or more!  We then ask them to test the KH levels in their water and they nearly always report that they have a level that is below 4.0.  When Steve (AKA “The Fish Dude”) joined our team after having spent his entire career to date in the aquarium industry, he couldn’t believe that aquaponic growers weren’t paying attention to KH levels.  Aquatic professionals know that dKH is key to a healthy fish environment.

Second, maintaining a buffer is critical for bacterial health.  If you get to the point where your system carbonates are completely depleted, your system pH can “crash” (decrease rapidly).  If it does,  your beneficial bacteria will quickly die and biological filtration will stop entirely.

Third, if you don’t have at least a minimal buffer of 4 dKH established in your system, you will need to manage pH on at least a daily basis (i.e. measure it and adjust as needed).  A natural result of the nitrification process is nitric acid, which continually eats away at your carbonate buffer.  If there is no buffer to offset the acid, the acid will simply lower your pH, unimpeded.  So not only is a lack of carbonates dangerous to your fish and bacteria, but it will also create a maintenance nightmare for you!  We often get calls and emails from customers who have a hard time raising their pH.  Insufficient carbonate levels is usually the reason why.

So why do some serious aquaponics growers strive for zero carbonates and instead use hydroxide-based compounds to raise pH?  As I understand it, they have two complaints about establishing a carbonate buffer.  The first is that it makes it more challenging to raise and lower pH, which means they have less pinpoint control over the pH levels of their systems.  While this issue may make sense if you are a large commercial farm and have an automatic pH adjustment dosing system, the people we work with don’t want or need that level of control over their pH.  We are after all, trying to establish an ecosystem in aquaponics so we can keep maintenance to a minimum!

The second reason is that un-maintained buffers may eventually be entirely consumed which in turn may lead to a pH crash in your system.  Again, while this is true, it is no reason to avoid establishing a buffer in the first place since without a buffer, pH crashes become much more likely!  It just means that you need to monitor your carbonate levels and build them back up if they drop below 4.0 dKH.

Here is what we recommend. GH and KH kit

  1. 1. Get an API GH and KH Test Kit either from us, or someone else, and figure out what your carbonate levels are. 
  2. 2. If you are above 4 dKH, then you should be fine for now but be sure to retest weekly as part of your normal testing regime.  Remember that as your system matures, it will create more and more nitric acid so your cargonate levels will drop over time. 
  3. 3. As you approach a dKH of 4 or lower, we recommend adding potassium bi-carbonate (AquaBuffer) to your system at a rate of 2 ½ teaspoons (12 ml) per 100 gallons of system water for each dKH level you need to go up. 

That is it.  Your system will benefit from both increased pH stability and increased potassium levels.  And your fish and bacteria will thank you!

24 thoughts on “The Carbonates Controversy in Aquaponics

  1. Just starting to put together an AQ garden in NY North Country. Overwhelming or
    daunting are probably too strong an adjective, but the more I research on the net it sends caution flags up. Any suggestions to narrow down difference in approaches?

    • LOL – I hear you, Jim, which is why I wrote my book. I figured if I was going to take all the time that I did to synthesize the “wheat from the chaff” that I might as well go the extra mile and write a book about it. ;-) My best advise is to find someone who is creating educational content that you trust and follow that person’s methods and ignore the rest. Otherwise you will get screwed up by the conflicting information.

  2. Thank you, thank you for this valuable information!
    I have a barrel aquaponic system and have been haing the gnawing problem of low pH over some time now. I have been adding lciluted garden lime to my system to raise the pH every other day or so and have been wondering about how to buffer my system. I will measure the carbonate level and go from there.

    • You are welcome, Arlene. If you get a decent buffer built (dkH > 4) you should only need to mess with your pH once a week or so….if that. I suggest moving over to carbonates to push up your pH as well. That is what our AquaUp product is based on.

      • Thanks. My KH is 3.0 and my GH remains orange even after 12 drops of the GH solution. I am assuming that my GH is way high. So I do need to buffer and thinking of getting the KH up to 4.0 at least for goldfish. Your Aqua up has calcium and potassium carbonate in it. Since I have been adding quite a bit of calcium to my system in the form of Lime. should I use just potassium carbonate to up the pH? Or do I need to add the calcium carbonate too?

        • Hi Arlene. If you’ve just been adding lime, and no potassium compounds, then you can just add potassium for a while – hard to say how long without doing a test of potassium and calcium levels in your system, though. And you might want to consider dosing with potassium bi-carb – our AquaBuffer product – first to get your KH level up a bit, and then switching over to AquaUp to go back to dosing with both calcium and potassium. Otherwise they can get out of balance with each other in the long term.

      • Just a question if pH is too low and a buffer is used wouldn’t it just maintain a low pH, i.e. buffer the low pH from increasing?

        But what if pH is low…can I buffer or I need to raise it before?

        And what is a safe way to raise it if I dont want to use KOH and CaOH?

        • I”m no chemist, but my layperson’s understanding is that rather than freezing pH at a certain level, buffers settle in at a pH range specific to the buffer type. Carbonate buffers are considered “weak base” buffers and will generally stay in a nice pH range for aquaponics. It is safest to raise your pH using potassium carbonate and calcium carbonate.

  3. I am also in the process of starting my aquaponic system. I do not understand why there should be a controversy regarding using buffer system in the water. In human, we have a built in buffer system. In natural pond, they also have a buffer system in place. If we are trying to recreate nature, then a buffering system should also be added. Why do we need a buffering system? A buffering system keeps the pH within a narrow range so there is no wide swing in pH. Most fishes and plants grow best under a narrow pH. It is true that they can tolerate some wide swing in pH but SLOWLY. Acute changes is what cause the death in fishes and plants. Different buffering system, maintain pH at different ranges. In the buffer system that we are discussing, it is optimal for fishes and plants. You can overwhelm a buffer system till it can not compensate any more. When that happens, you will see acute drop in pH or acute increase in pH depending on if there is to much H+ or OH- in the system. It will not “lock” a system in the acidic or basic range if you overwhelm the buffers. If the system is too acidic, then you add base to bring pH back up and the buffer system will start working. If the system is too basic, you add acid to bring down the pH and the buffer system will start working again. Why do we need to maintain optimal pH? It is because the enzymes in living things work best at the pH to keep life functioning. Below or above the optimal pH, these enzymes will breakdown, be disabled or work less efficiently. Some of these enzymes have critical functions in making energy, excreting dangerous toxins from the body or transport food to the cells. Biology 101.

  4. Our expanded clay balls in our grow beds are covered with a gritty while compound that looks like a salt. Now our plants are beginning to get white marks in the leaves, not a white mildew on the outside of the leaves, but actually in the leaves. We have used cc and pc to raise the ph when it falls to 6.4, and have used potassium bicarbonate as a buffer. Are any of these compounds causing this white “salt” on the clay balls and the white lines and spots inside the plant leaves. Plants look healthy but no one would want to eat the leaves of the herbs or lettuces looking the way they do. Please help. Our garden has been cycled and planted for over 6 months, and this white salt has been present for the past 5 months.

  5. Thanks for the great book Sylvia. As many here have done, I’m also new to aquaponics. I currently have a 100g tank with 50g sump “outside” with my first 4’x4′ GB inside. It’s been cycled for weeks now and all levels are generally where they should be. I do fight with the pH every day however. I see so many pH products on the shelf using the term “buffer”, but so far the ones I’ve tried seem to simply raise the pH (as I needed) and then it plummets, as you indicated in your well-written article.

    Question: Your “AquaBuffer” product does not seem to indicate, unless I missed it, how high it will raise the pH. What’s the highest level AquaBuffer will raise the pH?

    The current pond “pH Buffer” product I’m using brings my “clean-standby” water up to 8.x, so I use that very sparingly for now, as I’m learning. Thankfully my gold fish are more tolerant of my mistakes, so far. I’m attempting to use egg shells for now to buffer the system, until I can get your buffer bags or other shell material.

    Thanks again!

    Keep up the great info.

    • Thank you for your kind words, Chris. Much appreciated.
      We’ve been finding that the AquaBuffer product raises pH to about 7.2 – 7.4, which is a much better target than the product you are currently using. You might want to try it. ;-)

  6. I added egg shells in a netting to my radial filter to allow for some calcium carbonate to be absorbed and raise my pH gradually. I was shocked to see that from the shells of only one egg my 170 gallon system had a pH of 7.6 (from 6.6). The fish were fine and very active and did not seem stressed out from the pH swing. However, the result that baffled me was that my water hardness remained at 30 parts per million despite the addition of the egg shells. How is this possible? I do not understand how the pH can go one point up but the CaCO3 levels remain the same…

    • Hi Nadeem. The eggs dissolved the calcium precipitated out via the media as white build up or it is still in the water column which you can easily test for or the carbonate raised the pH. I forget what saturation levels are for fresh water but its not very high so its one of the first to find its way back out of the water as a hard water stain. General hardness is not just calcium so that being at 30 and not moving much isn’t surprising. I also thinking you might be confusing GH and KH.

  7. It seems like our system is consuming more kH / bicarbonate than we can supplement. In less than a month I have added 15 teaspoons potassium bicarb. Is it possible to put too much potassium bicarb into a system? Our kH levels are still much too low. I want to get it into the ideal range so I don’t have to worry about low pH and diurnal swings. Thank you! Loved the book and keeping up with the great updates on the blog.

    • Hi Arthur. We actually struggle with the same thing here. The risk is that you get out of balance by adding a ton of potassium, w/o adding calcium. Be sure to also add in some calcium carbonate or you will become calcium deficient.

      • Sylvia, thanks so much for the feedback! Our water is hard, so I will continue to add the potassium bicarb.. it seems to be working to regulate our pH although our dKH isn’t ideal. Added bonus is lots of flowers too!

  8. Hey Sylvia,

    Thank you for the great article on hardness. Is there ever a chance of their being too high GH/KH levels in a system? Our system is run off a well and is fairly mature (+1year) and good sized with almost 6000 gallons…We have been struggling with pH since the beginning and now it seems to be steadily climbing, now at 7.6-7.7. Interestingly enough, pH rises a few points after leaving our media bed and passing through our DWC troughs. It will go from 7.4 to 7.6 ish! We are experiencing some nutrient lock-out at these pH levels.
    Any help would be most appreciated!!


  9. Hello … carbonate hardness is key for pH stability!
    You discover my problem! I have this problem for many years with tap water! Karma for you!
    Every plant what I love ! thanks you !

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