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Fishless Cycling refers to the practice of establishing a new fish tank without the standard use of feeder fish or other cheap hardy fish. This can be done by adding ammonia to culture the bacteria that is necessary to maintain a healthy balanced aquarium.

Neccessary Reading: Nitrogen Cycle, The Everything Guide to Fishkeeping.

In a modern aquarium the water is filtered physically, chemically and biologically. This removes not only debris from the water but also harmful chemicals and contaminants.

The biological portion of the filter is made up of bacteria that consumes ammonia and nitrites. It takes a fair amount of time to establish a large enough colony of bacteria. Usually three to four weeks, sometimes as high as six weeks. During this time in traditional cycling many fish die because of the high ammonia and/or nitrite levels, both are fairly toxic to fish. Avoiding these unnecessary deaths is the goal of fishless cycling.

Two things are needed to begin the process, Ammonia and bacteria. The ammonia can be purchased but must not contain any other harmful chemicals. Shake the bottle, if it bubbles or foams its no good. I purchase mine at Walmart, $1.89 for a gallon. The bacteria is present in the air and will eventually appear in the tank. The key to shortening the process is to introduce a larger quantity of bacteria at the beginning. This can be done by getting filter material, gravel or water from an existing cycled tank. Adding aquatic plants also speeds up the process.Commercial products exist to speed up the process but I haven't heard of any that really work. Oh and you will also need a testing kit to check the ammonia and nitrite levels during this process.


I like to initially spike the tank with enough ammonia to get to 5-6 parts per million. The amount will vary according to the concentration of your ammonia, add some then test the water. The levels will stay high for a week or so and then slowly come down. When it gets close to zero add another dose. Eventually you want the entire dose to be consumed in less than 24 hours.


The Nitrites will go up as your ammonia eating bacteria get established. This bacteria are much slower to reproduce, it may take a few weeks to lower the nitrite levels. Be patient!.


The process is over when both Nitrite and Ammonia levels reach zero. At this point the tank is "cycled" and ready for fish. The bacteria colony should be large enough to support a fully stocked tank. Before adding fish do a 20% water change to clear up any Nitrates that have built up. And monitor the ammonia and nitrite levels for a few weeks just to be safe.

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