Biologic Cycling of the New Tank
Now, that the tank looks set up, youíre only half way home. Now, youívegot to get the water and the filters ready for the fish. Not only do the filters remove visible debris from the water; they also remove the poisonous chemicals from the water. The charcoal in the filter does a pretty good job of absorbing most of the toxins, but a big player in the filter processis the nitrifying bacteria.
You need to start growing a colony of bacteria to process the ammonia in your tank. Fish waste and dead plants breakdown into ammonia. The only way to keep the fish from being poisoned to death is to have and established filter of bacteria to break the ammonia down into poisonous nitrites. Of course, there are also bacteria that can break down the nitrites into nitrates. Once youíre there, the fish are happy.
Oh, Youíve never cultured bacteria before? Donít worry, theyíll growon their own, given the right conditions. You can use some "feeder goldfish" as starter fish to get your tank going. Most pet stores sell cheap goldfish to fishkeepers as food for larger carnivorous fish. One of these guys for every 10 gallons supplies enough waste to get you going smoothly. You might consider some danios to do the same job. They arenít as dirty as the goldfish, but you can keep them in your tank with your tropical fish. The goldfish will have to be deported, as they donít make suitable tankmates for your tropicals. I bought 3 "feeders" for $0.10 each. They'll get moved to the pond in a couple of weeks.
Itís best to have a test kit to monitor the ammonia, nitrate, and nitrite levels. Using your test kit you can watch the ammonia level rise until the bacteria starts eating it and producing nitrites. Next, you'll see the nitrite level peak and then start to fall. That's the sign you've got the right bacteria to process the nitrites. Finally, you'll see the nitrate level start to climb. The nitrates are relatively harmless to the fish. Doing a 20% water change every couple of weeks should keep the nitrate level to a reasonable level (<20-30 ppm).
The ammonia level should rise gradually until a peak around 10 days. The nitrite level will start after about a week and peak about 20 days. It all depends on your tank and if you got lucky and some bacteria heard your open invitation to come inhabit your filtration system.
Itís best to have some gravel or filter media from a well-established tank to culture or get a sample of the bacteria. If you have a buddy with a fishtank, you could get a used filter bag from him. If you want you can just put some "starter fish" in your tank and wait 3-4 weeks. Afterthat, you should have a cycled tank.