The nitrogen cycle in a marine aquarium (as in freshwater aquariums) is a chain reaction resulting in the growth of several species of nitrifying bacteria, each with their own job to do. The three nitrogen containing compounds involved in the nitrogen cycle are ammonia (NH³), nitrite (NO²-) and nitrate (NO³-). In general, the nitrogen cycling process usually takes about 30 days, but there is no exact time frame for this process, as each aquarium is different. Factors such as how many fish, invertebrates, and organic matter is present in the aquarium can vary the cycling time. Testing your aquarium water during cycling is very important, as this will tell you what phase the aquarium is in during the process.
The nitrogen cycling process starts as ammonia is introduced into the aquarium by adding a few fish. Ammonia is produced in many ways. It not only comes from the waste of live fish, but all other marine animals and organisms, as well as dead or decaying matter, including plants. Why do you think it is so important to remove excess uneaten fish foods, dead animals, or decomposing plant matter from an aquarium as soon as possible? They are contributors to a rise in unwanted ammonia in aquariums. Also, why is it important to not overfeed your fish, especially during the cycling period? More food = more waste = more ammonia!
Now during the cycling process, certain bacteria convert ammonia into nitrite, and at various stages both of these elements build to toxic levels, which endangers the lives of the animals. Do you see the Catch-22 here? If fish are needed as the source of ammonia to start the cycle, and during the process the ammonia and nitrite reach toxic levels that put them in harm's way, which many aquarists do not want to do, how can you cycle the tank "without" the fish?
Tank Cycling Options Without Using Fish
- Add some hermit crabs and/or other crabs instead. They are hardy animals, rather inexpensive, and will cycle your tank just as well as fish do. Besides, they can be pretty entertaining critters to have. Just feed the hermit crabs and true crabs either flake, pelleted or frozen fish foods and they will do the rest, starting to produce the ammonia you need to feed the bacteria.
- Cycle the tank with live rock and/or live sand. These are both living parts of the reef that produce waste. Not only will they cycle the aquarium, they become a source of biological filtration itself. When you use live rock or live sand that has come from a cycled tank, they already have the live bacteria (Nitrosomonas, Nitrospira, and Nitrobacter) needed to complete the nitrogen cycle. There won't be a huge population of these bacteria, so make sure to add live critters to your tank slowly until the beneficial bacteria population has a chance to grow.
- Add ammonium chloride. Read John Tullock's " Cycling the Tank" article, or refer to Martin A. Moe, Jr.'s book "The Marine Aquarium Handbook: Beginner to Breeder" for step-by-step instructions on how to use this cycling method. There are commercial ammonium chloride products available for adding to an aquarium for cycling. Do not use household ammonia for aquarium cycling unless it is clear and non-sudsy.
- Use the Cocktail Shrimp Cycling Method, which involves putting a few frozen cocktail shrimp in the aquarium and letting them decompose, creating ammonia in the process. As the shrimp decay they will produce enough ammonia to start the cycle, and when the cycle has completed (nitrate present and nitrite reduced to zero) remove what is left of the shrimp, do a partial water change, and start slowly adding your livestock to the aquarium.
Did you know there are ways to speed up the nitrogen cycling process rather than having to wait around for nature to run its course? See the other articles for more information.
Aquarium Water Quality: Nitrogen Cycle. Florida Department of Agriculture and Consumer Services.