Your tank is fully cycled once nitrates are being produced (andammonia and nitrite levels are zero). To determine when the cycle hascompleted, buy appropriate test kits (see ) and measure the levelsyourself, or bring water samples to your fish store and let themperform the test for you (perhaps for a small fee). This processnormally takes anywhere from 2-6 weeks. At temperatures below 70F, ittakes even longer to cycle a tank. In comparison to other types ofbacteria, Nitrifying bacteria grow slowly. Under optimal conditions,it takes fully 15 hours for a colony to double in size!
Cycling a fish tank - Petco Community - 76100
A large water change (50-70%) should be done before adding any fish to the tank to lower nitrate levels, which can be a pain to bring down later. When changing the water during a fishless cycle, do NOT use dechlorination that also sequesters ammonia, such as the very popular Amquel. I have heard from at least one individual who did everything right with regards to cycling her tank using this method... the tank cycled quickly, then she did a water change, then added a reasonable fish load the following day with more than adequate filtration, and observed both an ammonia and a nitrite spike. The only explanation that I could think of after questioning her extensively led back to the Amquel. In a normal, established fish tank, the ammonia is being generated nearly constantly... in a fishless cycle, however, the ammonia is added as a daily dose... IMO, it's conceivable (though not really provable unless a lot more people experienced identical problems) that the Amquel temporarily deprived the bacteria of its food source, causing a minor die-back in the colony at the worst possible time... right before adding her fish. To be on the safe side, use a simple chlorine/chloramine remover which does not affect your ammonia levels.
How to Cycle a Fish Tank - YouTube
Test the water at regular intervals to determine the levels of ammonia and nitrates. That indicates whether the ammonia is changing at the desired rate. Do that by using an aquarium . It is usually necessary to achieve a level of 8 ppm of ammonia in the water before the bacteria begins the cycle that establishes the correct water quality. It may be necessary to add more ammonia to the water after a day or 2 to feed the newly established bacterial culture. Allow the cycle to work until the nitrate levels fall back to at least 0.25 ppm before adding fish to the tank.
HOW TO CYCLE A NEW FISH TANK IN 1 WEEK! YES, 7 DAYS! | eBay