Aquaponics Nitrifying BacteriaI first wrote about Fishless Cycling for aquaponics systems in November, 2010 based on research I had done in cichlid raising, and since then it has become a generally accepted way to start up an aquaponics system. However, over the past year and a half we have improved the technique. I’d like to share our current thinking here so that those of you who are just starting out have the ‘latest and greatest’ instructions for getting your aquaponics system up and running.

Rather than repeat the first part of my original post, which is still completely accurate, I will simply link to it here. The modifications that I have in mind start at the ‘Instructions for Fishless Cycling’ section at the end of the post.

Instructions for Fishless Cycling – revised

Once you have identified your source of ammonia you are ready to start the cycling process. Just follow these simple instructions.


  1. Add ammonia to your fish tank until you get an ammonia reading between 2 and 4 ppm.
    • If you have a fish tank that is smaller than 100 gallons, I recommend adding only – a teaspoon, or less, at a time, then testing. Half a teaspoon of ammonium chloride (a powder), should give you close to 3.4ppm of ammonia in 100 gallons of water. It will take about 5 teaspoons of 10% Clear Ammonia to reach the same target of about 3.4 ppm. Given these two data points you can extrapolate about how much ammonia you should add for the volume of water you are cycling based on the strength of the ammonia you are using.
    • If your tank is larger than 200 gallons you can add more than 1 teaspoon of ammonium chloride at a time. To gauge how much, note that a teaspoon of Ammonium Chloride powder in 200 gallons of water will give about 3.4 ppm of ammonia. If you are using a 10% aqueous solution, adjust accordingly per the instructions above. If you are using powder, let the powder mix by running through the system for a couple of hours just to be very safe and then re-test ammonia. A liquid will integrate more quickly.
    • If you add too much ammonia (i.e. the ammonia test shows more than 6 ppm), drain some of the water in your tank and dilute the remaining tank water with fresh water. NOTE: If you see zero ammonia on your test you may have added far too much and ‘overwhelmed’ the test. Try retesting with a highly dilute version of your tank water.

Every day thereafter until your system is cycled

  1. Test your water for ammonia, nitrites, and pH levels and record them.
  2. Adjust pH to get it back to 6.8 – 7.2 if necessary (pH up to 7.8 during cycling is fine as long as you have not planted your system yet).
  3. Add ammonia to get the ammonia level back to 2 to 4 ppm if it has dropped (If it has, that is good news! It means that nitrifying bacteria has found your grow bed and begun eating your nitrites.).
  4. If you are seeing measureable amounts of nitrites then start measuring nitrates as well (Nitrates are the next step in the cycle).
  5. As soon as ammonia and nitrites drop to close to zero AND you are seeing measurable levels of nitrates, you are fully cycled and ready to add fish. Once you have added fish you can stop adding ammonia – the ammonia from the fish waste replaces the ammonia you have been adding to feed the new bacteria.

(If finding ammonia, seaweed and bacteria sounds like a pain, then we can help! At The Aquaponic Source we carry Cycling Kits with ammonia and seaweed, and Speed Cycling Kits that also include bacteria!)