Aquaponics 101 – Maturing Systems

I have spoken at length in the past about water tests to determine if your Aquaponic (AP) system is working, but I thought that I’d show you some results today of two systems working side by side, but at different stages in their maturity.

Let me recap a bit on what I mean by “maturity” insofar as it affects AP systems. The idea of a biological filter (in our case the gravel growbeds), is to encourage the growth of nitrifying bacteria to convert highly poisonous Ammonia to (slightly less poisonous) Nitrites and then to (much less poisonous) Nitrates. The Nitrates are what we need as nutrients for our plants. These two separate bacteria take time to mature and start doing their jobs, so by doing water tests we can determine at what stage our bacteria colony finds itself.

Let’s start with a mature system. Here are the test results from my home system, that I have converted to a hatchery, producing fingerlings year round.


As you can see, the Ammonia is very low, despite the fact that the fish had just been fed an hour or two earlier, and reads a mere 0.1

The Nitrites are Zero but there appears to be excess Nitrates (75). The pH is a healthy 7.0

These readings indicate that although the system is mature and the nitrifying bacteria is well established, there are excess nutrients in the system that need to be “mopped up” by planting more plants.

The water temperature is a toasty 26 deg C, water clarity is clear and the fish seem very happy.

Now to a “newish” system. I featured the building of this system on the 11th of March and you can see it here


The high Nitrites reading (about 0.3) is a dead giveaway that the system is new. The bacteria that convert Ammonia to Nitrites is not properly established and this reading will (hopefully) drop. There are some Nitrates coming through (25) so the plants in the growbed are happy enough.

The pH of 8.5 is a mystery and I will have to monitor this. The water temperature of this system is 19 deg C as it is outside and not connected to my heat pump.

Hope this is helpful to you.



11 Responses

  1. Is the raw water alkalinity not a bit high indicated by the higher Ph?

    • The nitrifying bacteria tends to pull the pH the other way so I don’t mind it on that side. Normally we have to buffer the pH with oyster shells. Thanks for your comment.


  2. Where did you get this test kit? I want to get one!

  3. Hi Tom,

    Any good pet shop should have one. Just ask for an aquarium test kit. It works for fresh water or marine aquariums. The tests that you need are Ammonia, Nitrites, Nitrates and pH. Also ask for DO (dissolved oxygen).



  4. I’ve been running a system for about 6 months and have not been able to get the nitrate level high enough to support plants. I have eleven 3-4 inch Koi in a 17 gallon tank with a Fluval biofilter that is rated for up to 40 gallons. The ammonia and nitrite levels fluctuate occasionally, but are usually low. But, the nitrate level never seems to get above 10ppm according to the test kit. I have been adding fish to raise the levels, but have not seen what I expected to see. Any suggestions?

    • Hi Doog,

      The problem seems to point to a pH or temperature issue. When next you do tests, measure Ammonia, Nitrites, Nitrates pH and temperature at the same time and post the results. I’ll bet one of the two beneficial bacteria are not happy. Also, how much are you feeding? Increase the feed slightly and see if you can force up the Ammonia.


  5. The ammonia is going up, but like you say, the bacteria are not happy. My pH stays too low at 6.5 or so. When I add pH Up, I’ve noticed the EC of the water increases. I have a pH and EC meter that I test the pH and have noticed the salts climb. I moved into a new house where the temp is average 60-65F. At my old house the temp was 75-80F, but I had the same pH problem. I’m going to get some heat, but what should I do about the pH and the additives to regulate that? Thanks for your help.

  6. I started using calcium chloride, epsom salts and baking soda to in crease the hardness and alkalinity of the water. Now the pH is more stable and the bacteria are happy and doing a great job.

  7. I’ve now switched to Calcium hydroxide to increase hardness.

  8. My ammonia is low and nitrates are acceptable but the nitrites are maxed.

    • Hi Steve,

      From what you describe this is a typical system in the middle stages of maturity. There are two seperate type of bacteria at work here. Nitrosomonas which converts Ammonia to Nitrites is obviously hard at work.

      The next bacteria needed, Nitrobacter is clearly not firmly establised yet. This will convert the Nitrites into Nitrates which the plants will take up. All that is needed now is a bit of patience.

      “Build it (Nitrites) and they (Nitrobacter) will come.”

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