here is an article that i wrote for another forum that i mod on.
cycling is the first step to starting a fish tank. there are basically two ways to cycle one is to start with adding ammonia to jumpstart the tank. the other is to add fish to start the cycling. with a fishless cycle you need to start the cycling by adding some element other than fish to start raising the levels of ammonia. ammonia is created mostly by fish waste, uneaten food or decomposing plant matter. you can acheive this by one of two ways. either purchase ammonia and add it by drop til the levels of ammonia are raised. you can tell if the ammonia is raised by using a test kit that should be on hand whenever keeping fish. the ammonia should be pure. if you shake it and it bubbles it is not pure but has additives to it. another way is to feed the empty tank letting the food decompose on the gravel bed. ammonia is then turned into nitrites. nitrites is a lesser concentrated form of ammonia. still harmful to fish but not as harmful as the purer form, ammonia. once the levels of ammonia peak, the levels of nitrites should start to raise and the levels of ammonia lower.
the nitrite step is important as this is where the nitrifying bacteria is formed. this is also called the beneficial bacteria. nitrobacter and nitrosomona are the two beneficial bacterias that are present in the gravel bed and other elements of the aquarium such as the filter medium and water. the greatest amount is detected in the gravel bed. when maintaining the aquarium after cycling, you want to make sure that you do not vaccuum to far into the gravel bed. this can remove the bacteria and cause the tank to go into a minicycle. a minicycle occurs when the beneficial bacteria cannot handle the load of the tank and must multiply to rid the tank of nitrites. this bacteria feeds on the nitrites in the tank.
nitrites are then turned into nitrates. the lesser concentrated of the three. nitrates are essential in planted tanks. aquatic plants feed on nitrates. faster growing plants require higher levels of nitrates than slower growing ones. once the nitrates have risen plants can be introduced to lower the levels of nitrates.
once the ammonia, nitrites and nitrates have peaked and lowered and remained at zero, the tank is considered cycled. the biological filter has been established to handle the load of the tank. some aquarists will experience a bacterial bloom. this is a milky white cloudiness to the tank water. blooms will normally dissipate in a few days. fish can be introduced slowly so the bacteria colony can increase to handle the higher amounts of waste produced by the fish.
semper fi