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 such as AquaBuffer.  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!



  1. Jim Maceda February 7, 2014 at 4:27 pm

    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?

  2. Brent Johnson February 8, 2014 at 1:19 pm

    Thank you for explaining this issue in a way that is very easy to understand.

  3. Sylvia February 8, 2014 at 2:18 pm

    You are most welcome! I just put out a video on aquaponics pH and carbonates as well that you may find useful.

  4. Sylvia February 8, 2014 at 2:21 pm

    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.

  5. Brent February 8, 2014 at 3:22 pm

    Oh cool. Yes I love the videos

  6. Arlene February 10, 2014 at 3:44 pm

    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.

  7. Sylvia February 10, 2014 at 3:54 pm

    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.

  8. Arlene February 13, 2014 at 2:01 am

    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?

  9. Sylvia February 13, 2014 at 12:03 pm

    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.

  10. Arlene February 14, 2014 at 12:07 am

    Thank you.

  11. chan February 27, 2014 at 3:50 pm

    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?

  12. Sylvia February 27, 2014 at 5:17 pm

    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.

  13. Steven Lin March 26, 2014 at 3:57 pm

    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.

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