You have to test the water. The best way to do this is to buy a freshwater master
test kit, which will allow you to test for
ammonia,
nitrite, and
nitrate. When your tests show that ammonia and nitrite are both 0, and your nitrate is something other than 0, your cycle is done. Another way is to take water samples to your
LFS and have them test it for you, but quite honestly I would avoid that if you can...it is kind of scary how many people have posted about the terrible cycling advise they got from their lfs when they took water in for testing. A test kit is not all that expensive, and the tests are very easy to do yourself.
http://www.bigalsonline.com/BigAlsUS...rmastertestkit