Actually, the process of “cycling” does not begin until fish or a culture of nitrifying bacteria are added to an aquarium, but the longer you wait to add the first fish after initially setting up your tank, the better. Most aquarium experts recommend waiting at least 48 to 72 hours. Always check temperature and test for pH and ammonia first, as many municipalities add chloramine to tap water and a single dose of water conditioner does not always fully neutralize the ammonia.