posted 02-13-2004 08:06 PM         

But I'll also give a quick summary.

Nitrogen cycle:
Fish produce ammonia which is toxic to them. In an established/cycled tank there are 2 types of nitrifying bacteria. The fist converts ammonia to nitrIte which is also toxic to fish. The second type of bacteria converts nitrIte into nitrAte which in levels below 20ppm is not harmful to fish. And the only way to get rid of nitrAte is by either having a ton of live plants (really not an option with oscars) or doing water changes.

Fishless cycling:
Cycling a tank is the process of allowing those 2 types of bacteria to form colonies in the filter media (there will also be bacteria on all the surfaces in the tank, but the majority is in the filter).

There are two reasons for doing a fishless cycle as opposed to cycling the tank with "sacraficial fish" The first is because cycling a tank involves VERY high levels of ammonia which will kill a fish. This is very cruel to the fish and their deaths can be avoided by doing the fishless cycle. Secondly, by dong a fishless cycle, you can be sure that you have grown bacteria colonies sufficient to handle just about any fish you put in there. If you cycle a 75 gallon tank with a few goldfish, they're not going to produce near the bioload of 2 oscars so your bacteria colonies won't be sufficient and the tank will go though a mini cycle when you add the oscars.

So, the main point of a fishless cycle is to simulate the presence of fish w/o actually having them in the tank. First, like Puff said, you will need to set the tank and all it's equipment up then follow the instructions in the article I linked to.

For a 75 gallon tank it will probably take about a month to cycle. Just be patient and wait until it's done before adding your fish.

Also, if you can get some gravel or filter media from an established tank, that will help to speed up the cycle a little (as long as you don't rise it off with chlorinated water or let it dry out).