Fishless cycling is the process of cycling a tank, or establishing a biological filter in a fishless aquarium.
The biological filter, or nitrogen cycle, naturally occurs over the first 4-6 weeks after a tank is set up. Cycling a tank is necessary to keep the water free of pollutants and the fish healthy, but while the filter is establishing itself, fish are exposed to toxic levels of ammonia and nitrite and often succumb to disease and death. Fishless cycling removes fish from harm by establishing the biological filter before fish are introduced to the aquarium.
Normally, when fish are added to a new aquarium, even though the water is clean, ammonia begins to build immediately, as fish release ammonia through breathing and waste. Uneaten food, and decaying plants also create ammonia. However, ammonia is necessary to start the nitrogen cycle -- the first step in establishing a biological filter.
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In January 1999 Chris Cow who holds a PhD in organic chemistry, posted a paper online regarding fishless cycling. He got the simple idea to add ammonia to a fishless aquarium in order to get the nitrogen cycle going. This not only saves fish, but it saves the aquarist from stress as well.
At this point all of the normal phases of the biological filter can be triggered without worry. Ammonia levels can soar, followed by toxic levels of nitrite, until, finally, both become neutralized. With the tank fully cycled any ammonia created by adding fish will now quickly be converted to harmless nitrate by the established colonies of positive bacteria that make up the biological filter.
Chris Cow's experiment worked wonderfully, and has been used by countless aquarists since.
To use the fishless cycling method simply add 4-5 drops of pure ammonia per 10 gallons of water to a fishless tank. Do this once a day until nitrite becomes measurable. At that point cut back to 2-3 drops per 10 gallons of water, per day. When nitrite and ammonia are both at zero, and nitrate is measurable, the tank is cycled. A substantial water change of 25% or more is advised, then your tank is ready for a full complement of fish.
Only pure ammonia, without detergents or colors, should be used. Ammonia with additives will foam up when you shake the bottle. Pure ammonia will not foam.
A simple declorinator/de-chloraminer is recommended while cycling fishless, rather than products like Prime or AmQuel that sequester ammonia by converting it to non-toxic ammonium. The concern is that sequestered ammonia may be harder for bacteria to process, and therefore could slow down the establishment of the bacteria. Once the biological filter is established, adding products like Prime and AmQuel are excellent and will not hamper the biofilter.
Biofilter bacteria thrives at about 80 degrees Fahrenheit (27 degrees Celsius). If you turn up your tank's heater while cycling fishless, the tank can cycle in as little as 7-10 days. Be sure to turn the heater back down when the nitrogen cycle is complete, and allow the water time to reach the desired temperature before adding fish.
The great advantage of fishless cycling is that it is humane and stress-free. Another great advantage is that you can add a full complement of fish at once, because the biofilter is fully established. This is especially significant when keeping territorial fish that are better added all at once.
Other advantages include keeping a quarantine or hospital tank cycled in case of emergency, by simply adding a drop of ammonia to it each day to simulate the presence of a fish.
Any aquarist who has gone through the difficulty of cycling a tank with fish, will surely appreciate the fishless cycling method!