The Freshwater Nitrogen Cycle

This cycle is important for any aquarium owner to understand. The nitrogen cycle, if not completed, is what causes new tank syndrome, and new tank failures. The cycle begins with a new tank, with new water, without any fish. When the first fish is added, ammonia from its waste immediatly poison the water. Too much ammonia will kill your fish. However, the fish help certain bacteria to grow that will turn the ammonia into safe by products. The nitrogen cycle has three steps:

1. The Initial Step: This step occurs when fish are first introduced. Their waste and uneaten food is broken down into non toxic ionized ammonia (NH4) and toxic unionized ammonia (NH3). The non toxic NH4 is present when the pH of the water is below 7, but when the pH is above 7, toxic NH3 is present. Ammonia levels rise within the first three days. Any amount of NH3 is dangerous, but when it reaches about 2 ppm, your fish are at risk.

2. The Second Step: Nitrosomonas bacteria oxidize the ammonia, thus eliminating it and creating nitrites in the process, also toxic to fish. I mg/L of nitrites is lethal. The nitrites will appear around the end of the first week after adding fish.

3. The Third Step: Nitrobacter bacteria convert the nitrites into nitrates, which are non toxic in small doses. These nitrates should be monitered every month or so for the rest of you aquarium experience. At high levels, nitrates are lethal. However, they will always be present. Routine water changes will prevent these nitrate spikes.

The entire process should take around 2 to 3 weeks. When cycling, test water routinely to see how far along your tank has come.

In addition to previous knowledge, http://freshaquarium.about.com/cs/biologicalcycle/a/nitrogencycle.htm, was used to obtain information about the nitrogen cylce.