Fishless cycling is a term used to refer to a process of cycling an aquarium or for setting up a biological filter in an aquarium that does not contain fish.
The nitrogen cycle (which is what the biological filter refers to) would naturally establish itself in a tank over four to six weeks immediately after the tank has been set up. Cycling the water in the tank is an important step in order to ensure that the water inside is free of pollutants, which will also ensure that the fish will become healthy. But during the initial process of cycling a tank, the environment inside the tank is generally considered harmful to fish because of the increased levels of ammonia and nitrite.
This is an environment that can cause fish to develop different types of diseases or even cause them to die. By using a fishless cycling method, fish is not harmed because no fish is introduced until after the nitrogen cycle has been established.
In order to begin fishless cycling in a tank, four to five drops of pure ammonia per 10 gallons of water is introduced into the tank. The addition of ammonia is done once a day until nitrite has increased enough to become measurable. When this happens, the ammonia added is reduced to two to three drops per 10 gallons of water. When both the nitrite and the ammonia are now at zero levels, and the nitrate levels are now measurable, the tank is considered fully cycled. A water change of 25 percent is then performed before fish is introduced to the tank.