Iain Miller wrote:

Bear in mind that the bacteria that live in the filters need ammonia &
nitrites to feed on so you need some source of ammonia in your new tank - if
you put a mature filter into a sterile, clean tank it will actually die
back - so putting a few fish in at the same time is very much the way to go.
Check for ammonia & nitrites for the first week or so - you may never see
any if you do it right.


I'm happy you posted this. I've always had a tank around and have cycled
my tanks by using aged media. I read in other sources how it can take a
tank a month or so to cycle, but using the method you describe (with a
light fish load the first month) I've never measured an ammonia or
nitrite spike.

I would like to add that I would not slap in delicate fish or more than
two or so fish while the tank is settling in, even with this process. At
least until your fist scheduled water change.