What is the nitrogen cycle?
In nature, the nitrogen cycle is a process by which nitrogen is converted through various chemical forms. In an aquarium, the nitrogen cycle begins with ammonia which is introduced by fish and other animals through waste, decomposition and the respiration process. The toxic ammonia is converted to nitrite by special nitrifying bacteria. A second type of nitrifying bacteria converts the toxic nitrite into nitrate. Nitrate is much less harmful to fish than ammonia and nitrite, and is usually removed from the aquarium by preforming regular water changes.
How do I cycle my aquarium?
When setting up a new saltwater aquarium, the nitrogen cycle must be fully established before fish or other animals can be added to the tank. This process is known as cycling the aquarium. Once the tank is set up and the filtration system has started, ammonia can be added to the water by adding fish food, raw fish, shrimp, or the more precise method of adding ammonium chloride occasionally to the water. This is referred to as a "fish-less cycle", and we never recommend doing a "fish cycle". You will often read about adding a few damselfish to your aquarium ("Fish-cycle") as "sacrificial" fish to supply the cycle with ammonia. This practice is not only cruel to the fish, but many hobbyists will later need to remove the fish (usually a damselfish) from the aquarium due to severe aggression towards the more desired, new additions to the tank. We NEVER recommend using this method to cycle your tank.
You will need to monitor the ammonia, nitrite, and nitrate levels several times a week. It usually takes 2-8 weeks to fully cycle a new aquarium. DO NOT rush this process. It is better to err on the side of caution and wait a little longer. Rushing the process will only result in dead fish. The tank is fully cycled when ammonia and nitrite levels drop to zero and the conversion of nitrate is completed. When using ammonium chloride to cycle the tank you should see 1 PPM ammonia being converted to zero within a 24 hour period. This conversion will ensure that the cycle is completed and your biological filtration will easily handle the addition of a responsible amount of livestock.