"New Tank Syndrome", "The Nitrogen Cycle" or "Cycling a Tank" referrs to the period in which ammonia (fish waste) and then nitrite levels rise to dangerous quantities before being converted into relatively harmless nitrate. The largest mistake made by new aquariasts is to buy a tank, set it up, and three days later put in $300 worth of prize fish. If you havent "Cycled" your tank, your fish are in for a very hard ride for the next 30 days.

In aquariums ammonia needs to be broken down by benificial bacteria into nitrite, which is itself broken down by a different group of bacteria into nitrate. In a newly set up aquarium, those bacteria are not present, and it takes time (see below) for those bacteria to multiply to the point of being able to keep up with the waste output of the fish.

Even old tanks may have to be cycled. Removing large quantities of bacteria, by changing the aquarium gravel for instance, will cause an "old" tank to go through another cycle. Poisoning the bacteria with medicines or shocking them with chlorinated water or sudden temperature changes will also set the cycling process back to day one. New tanks are generally broken in by adding a few hardy fish and simply waiting out that first month. It is important to note that the cycling process does not begin until fish are added (except for alternate cycling methods such as liquid bacteria and feeding an empty tank).

Recommended fish for cycling: Smaller barbs (tiger, gold, rosy), larger tetras (head and tail light, red eye, red minor, buenos aires), danios (zebra, leopard, pearl, gold) and rasboras (heteromorpha, scissortail, redtail, brilliant) are hardy enough to withstand the temporarily high ammonia and nitrite levels and inexpensive enough to replace if some perish during a particularly rough cycle. Damselfish (blue, yellowtail, striped or dominoe) and mollies are their saltwater counterparts.

Once the cycle is in progress, it's best to not add other fish until it is complete and keep the water tempature from 78 - 82 degrees as colder water will cause the nitrogen cycle to take longer. The starter fish have had a chance to become slowly accustomed to the increasing ammonia/nitrite levels; any new fish have to deal with the shock of being dumped into poor water conditions all at once. It's also best to feed regularly, once or twice per day, but sparingly. Any uneaten food can worsen the already poor water quality. Periodic testing for Ammonia and Nitrite is necessary to determine where you are in the cycling process. Your fish may show signs of distress, including rapid breathing, loss of appetite, bulging eyeballs, bloat, fin rot and skittishness during the peak times of the cycle. It is not recommended to do any water changes through the cycling process.

Ammonia at any level is toxic to aquarium fish, and Nitrite is almost as bad. When your test kit showes no sign of either (0ppm) then you are safe to start adding your prize fish.

Put the fish in. Ammonia and nitrite readings remain at zero and water is crystal clear.
Toxic ammonia levels rise rapidly to dangerous levels and the benificial bacteria start to develop. Fish start to stress and loose their appetite.
Ammonia levels peak and bacteria begin to convert into nitrite. Fish show obvious signs of discomfort and some may die. (remove any dead fish as soon as you spot them).
Ammonia is being converted to nitrite immediatly and nitrite levels increase rapidly. Your fish seem happier (for now).
Nitrite levels peak. Fish are stressed again and only the strong fish will survive the long term exposure. If necessary, you may do a 20% (no more) water change at this point.
Nitrite levels slowly begin to decline, and the second stage of the cycling process begins. Fish become more stable.
Nitrite levels drop rapidly as it is converted to nitrate.

No trace of ammonia or nitrite, the tank is now cycled. You may do a 30% water change and add your prize Cichlids (or whatever).

Many hobbyists do not recommend exposing Cichlids to nitrate levels above 30ppm for any extended legnth of time. Usually a 20 - 30% water change weekly is advisable for a well stocked tank of African Cichlids. Good Luck!