Nitrogen cycle and water changes in a slightly acidic tank?

Question

Hi. This is just a theoretical question right now but If I had a tank where the pH was 6.2-6.5 then wouldn't all (or at least the vast vast majority) of my fishes wastes be converted to ammonium (NH4) and not ammonia (NH3). And ammonium is not harmful to fish (except in exceptionally large concentrations) so you would rarely if ever have to do a water change. I just did a quick calculation but the ratio of ammonium to ammonia is more than 99:1.Did I just discover the laziest way to keep a fish tank or is something wrong with my theory?

Answer 1

You are correct, the vast majority would be changed to ammonium, but still, some of the ammonia would be converted to nitrites by the bacteria and then to nitrates.  Both are toxic to fish (but not as bad as ammonia) and still would eventually damage your fish.

Plus, keeping a tank at pH 6.2 would be almost as much work as doing the water changes.  Water changes are still the best way to keep a tank healthy and your fish happy and disease free.

Additionally, many fish do not deal well with that low of a pH too.  A few of the South Americans would do well, but you would probably not see the bright natural colors that many fish only display when the water conditions are correct for their species.

Answer 2

While it's true that ammonia is less toxic in acidic water you still need to process or remove it. And cycle bacteria grow slower in low pH  than high.

So although the ammonia is less dangerous, it's harder to process. However the nitrogen cycle will still get established eventually and convert the ammonia into nitrate that eventually needs to be removed with water changes.

In an established tank you dont do water changes to control ammonia, you let the filter process the ammonia into nitrate, then you do water changes to remove the nitrate.

Sorry - no free lunch, keep doing the water changes.

Ian