"David J. Braunegg" wrote in message
...
My ammonia and nitrites test out at zero, so my bio-wheel biological
filter seems to be working well. I'd like to figure out how often to
perform partial water replacements based on the nitrate levels. At what
level of nitrate should I do a water change, and what level should I try
to bring the nitrate down to?

Thanks,
Dave

It depends on size of tank and fish. A samll tank under 20 and large tanks
with messy fish may be 30/40. The lower the better. Some fish like angels
need regular water changes, 2 or 3 a week as they thrive in claen water
rather than the nitrate level. I do 2 x 10/15% a week on all my tanks, as
it prevents problems rather than spotting them later. In my 65g with 2
angels and 5 clown loaches they just deserve the best I can offer them, and
they are all thriving and growing. Some LFS say 10% a week or 20% a
fortnight, that that is a minimum/general rule and it's up to you to decide
based on your fish. Mary.