Question from Grower:
Over the past 5 weeks we have had a problem with extremely high ammonium. The reason we know this is we bought a specific ammonia tester and found it to be normal but it’s still a huge concern because I feel like the only reason it’s not converting to ammonia is our PH sits right around 6.0 and we make sure we aren’t making any additions that will push it above 6.2 and risking that conversion to happen. The biggest problem is we can’t figure out why. We contacted the manufacture of the HPPG to see if it’s possible that we lost to many beads but they didn’t think that was the issue. They did think it was flushing too often so be slowed that down. That was 20 days ago. Since that the ammonium has not really changed but we did have 2 days where the Nitrites started jumping up so I thought maybe that was bacteria building back up again. The nitrite is now sitting around .25-.5 for the last 3 days but still no change in the ammonium. It has been around now for that whole 5 weeks. Nitrates are always around 120. Our feed rate is 3150g per day which is below the filters rating. Another interesting thing is we see a change the day after big harvest days. We will get below 8 and then it will be right back up. Please let me know if you can think of anything I can do. Fish are acting normal, eating, swimming around jumping out of the water and very active.
Response from Tawnya:
Good to hear from you. Interesting about the change in the water parameters. First case, we always would look for something that would trigger high ammonia such as dead fish. We’ve found dead fish in our pipes before. As well, anything decomposing, algae, duckweed, plant material, roots, leaves, etc. will all produce some amount of ammonia as they decompose. In addition, if you are on city water, one thing municipalities do use is chloramine (and can change regiments without notice). Chloramine is when the city adds ammonia to chlorine to the water to disinfect it more effectively. Most carbon filters can only separate the chlorine and the ammonia which can cause it to be high (when it never was before). This can also be a problem even with good water filters if you haven’t changed the cartridges in the proper amount of time and they are no longer filtering out contaminants. If you are well water, we have seen high ammonia from tap water, but usually only in agricultural areas when they are applying spring fertilizers.
Ammonia toxicity is relative to the pH and the temperature. So the fact that you have low pH and the temperature is around 70F, means that the toxicity of the ammonia is a fraction of what you are seeing on the test results. I have attached the handout from class that explains how to calculate and includes the conversion table.
How to Calculate Un-Ionized (toxic) Ammonia
Based on your filter and the current nitrite and nitrate parameters, it doesn’t sound like you are denitrifying. When that happens too many heterotrophic bacteria build up in the filter, tank, pipes, DWC, media, etc. These larger bacteria are the ones that consume solids, they are bigger and out compete the nitrifying bacteria for space to live and oxygen. So if you have too many solids in the system that can cause ammonia to stop being converted.
I am wondering why you are keeping pH down around 6.0 – 6.2? We always tried to maintain pH closer to 6.8 – 7.0 for the health of fish, bacteria and plants. In addition, the nitrification process depends upon a carbonate source to be performed. Nitrification requires alkalinity – For every 1g of Ammonia-Nitrogen converted to Nitrate, 7g of alkalinity is consumed. If you don’t add a carbonate source like calcium or potassium (and it isn’t being introduced in significant quantities through top off water), then the bacteria will not be able to perform nitrification properly. Leafy green vegetables are happy with a pH around 6.8. Most iron supplements can be absorbed relatively effectively around 6.5 – 7.0 for those plants that need iron (basil, collards, kales, etc). Tomatoes like lower pH, but they also like phosphorus, so instead of keeping the whole system with low pH for them, we just add a small dose of phosphorus around their roots and avoid circulating their water for an hour or so until it is absorbed.
- So I would check for dead fish and other decay and remove anything found
- Stop feeding for a day or so to try and minimize continued ammonia build up
- Check the tap water to see if that might be the source
- Use calcium or potassium carbonate to adjust pH up and help bacteria convert ammonia more effectively
- Make sure that your ammonia test is actually reporting correctly (we have had single reagents go bad and show the wrong colors)
- If you are using some sort of digital probe device, make sure that it is clean and properly calibrated
Hope this helps. Let us know what you find out. We are always curious to know what’s going on and learn from others.