Ammonia is best added in a tank which has no fish. They are very toxic to fish if tank water has high pH. Low pH reduces the toxicity.blue_gourami45 said:Okay, here is the question: if you start your new tank by adding filter media from an established tank, should you not be adding ammonia as well? I recently upgraded from 25 gallons to 46 gallons, by using a handful of the old gravel and some filter media from the established aquarium to the new one, but I also used the Cycle product (which I know no one approves of). No fish loss!