In my opinion, the best way to cycle your fish that is by using the cycling with fish method. As I hate to see my fish tank empty for 6weeks!
First, a quick overview on what this cycle is and why it’s important. Basically, all of your fish are continually releasing waste into the water, most importantly in the form of ammonia. Ammonia is deadly to your fish in even small quantities. Luckily, there are bacteria that love ammonia and want only to consume it. This leads to another problem, though, the bacteria’s own waste product- nitrite. Nitrite is also quite harmful to fish. But, just as there is a bacteria that loves ammonia, so too is there one that loves nitrite. These bacteria then output nitrate which is relatively safe for most fish. These bacteria are very easy to grow, but, it takes time. Normally you would cycle a new tank sans fish, but, if the fish are already present then you’ll have to approach things a little differently.
To cycle your tank with the fish in, you’ll need to do big water changes (most of the water in the tank) every day, feed the fish very little to minimise pollution and regularly test for ammonia, nitrite and nitrate. And do extra water changes whenever ammonia or nitrite levels get too high.
How to Cycle a Fish Tank | Preparing Your Aquarium Ready for Fish
Goldfish Tank Setup: Cycling your goldfish tank - The Goldfish Tank
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 the section)and measure the levelsyourself, or bring water samples to your fish store and let themperform the test for you (perhaps for a small fee). The cycling 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!Of course, there are many variations on the above that work. However,it is a bit difficult to give an exact recipe that is guaranteed towork. It is advisable to take a conservative approach and not addfish too quickly. In addition, testing the water to be sure nitratesare being produced eliminates the guesswork of determining when yourtank has cycled.Standard test kits measure total ammonia (ammonia plus ammonium)without distinguishing between the two forms. The following chartgives the maximum long-term level of ammonia-N in mg/L (ppm) that can beconsidered safe at a given temperature and pH. Again, note that a tankwith an established biological filter will have no detectable ammonia;this chart is provided only for emergency purposes. If your levelsapproach or exceed the levels shown, take emergency action IMMEDIATELY.Should ammonia levels become high during the cycling process,corrective measures will need to be taken to prevent fish deaths. Most likely, you will simplyperform a sequence of partial water changes, thereby diluting ammoniato safer concentrations.In an established tank, ammonia should be undetectable usingstandard test kits available at stores. The presence of detectablelevels indicates that your bio filter is not working adequately,either because your tank has not yet cycled, or the filter isnot functioning adequately (e.g., too small for fish load, clogged,etc.) It is imperative that you address the problem (filter) inaddition to the symptoms (high ammonia levels).