I think everyone is partially correct, but not totally correct.1 - UV light will have no effect on nitrifying bacteria
2 - UV light will have no DIRECT effect on pH, KH, or ammonia.Here is where it gets complicated:
1 - If there is green water, the algae is removing a lot of ammonia before the ammonia reaches the biofilter, so the biofilter was only removing a portion of the ammonia.
2 - UV light kills planktonic algae.
3 - Dead algae no longer takes up ammonia.
4 - Decomposing algae releases ammonia, lowers O2, and increases CO2, which becomes carbonic acid.
5 - If the KH is adequate, the acid is buffered, the KH drops, and there is no effect on pH; however, if KH is low, the acid will cause pH to drop.
6 - The biofilter was not geared up for the new ammonia load and it will take time for it to come up to speed.
7 - The nitrifying bacteria grow more slowly at low pH.I agree with the treatment advice others have been giving, which can be summarized as follows:
1 - Bind the ammonia.
2 - Add baking soda slowly to bring the pH up to 8.3 over three days.
3 - Once the pH is 8.3, add enough baking soda to bring the KH up to about 150 ppm.
4 - If nitrites appear, add salt to 0.15%. (there is a 50/50 chance that you will have measurable nitrites once the ammonia goes down. It is possible that both sets of bacteria will recover simultaneously so that no nitrites will be seen - each pond is different).
