To cycle a tank, set the tank up with water, a filter and a small number of hardy fish. Change the water every two to three days, and test it regularly until there is no sign of ammonia or nitrates. Cycling a fish tank takes six to eight weeks to complete.Continue Reading
Put properly-prepared water, any desired plants and a filter into the tank. Select a few hardy fish of the type you want to keep. Make sure the number of fish is very small for the size of the tank. Doing so reduces the stress on the fish and the number of fatalities. Do not use goldfish to cycle your tank unless you intend on keeping goldfish.
Feed the fish carefully, and avoid overfeeding. The leftover food contributes to additional waste in the tank, which adds further stress to the fish. Change 10 to 15 percent of the water every two to three days. Continue to test the water at least once a week. The water can be tested with at-home kits or by taking a sample to a local pet store for low- or no-cost testing.
When the ammonia and nitrate levels in the tank drop to negligible or zero, begin adding more fish to your tank. Only add a few fish at a time, and give the filter a few weeks to adjust to new fish before adding more. Be sure to avoid overfilling tank or overtaxing the filter.