Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
A few days will not be a problem.
A week, and the population will start to drop.
Several weeks and the population will be quite low.
Depends on how many fish you will be quarantining. If you are getting a large order of fish, anything like a full bioload, then keep adding the ammonia, though it is OK to do really big water changes a day or two before the fish come, then not add any more ammonia.
If it is just a few fish, then you could allow quite a bit of the bacteria to die, and there would still be plenty to deal with the waste from just a couple of fish. Again, do as many or as large water changes as needed to get the NO3 way down. Water changes will not affect the bacteria (just remember the dechlor!)