The setup of a new aquarium involves a maturing process which is called nitrification. When an aquarium is first set up with new sand, water, etc., it is a sterile environment. This environment must go through a growth period in order to properly support fish and coral. During setup you wash the gravel and place it in the aquarium and fill the tank with new water.

At this time, both sand and water contain no beneficial bacteria which help support life in the aquarium. After the tank has been setup for 24 to 48 hours the  temperature should be stable. This is when the live rock should be added. Live rock is rock that has already been in an aquarium for sometime and will help start the growth cycle. During the next six weeks any excess waste produced by the live rock will fall into the sand bed and begin to rot. This rotting start to produce ammonia and the first bacteria begins to grow.
The ammonia cycle will last approximately 10 to 12 days. As the bacteria begin to consume the ammonia the toxic level is reduced, but the second cycle begins. The bacteria that eats ammonia produces another toxic by-product called Nitrite. The nitrite levels now start to build in the aquarium, and will continue to cause problems for about four additional weeks. During this second growth period, another strain of bacteria begins to grow which breaks down the nitrites into a relatively harmless by-product, Nitrate.

Once this cycle is complete you can begin to slowly stock the tank with live stock. Remember there are no short cuts to a healthy aquarium, and patience will save you fish and money!