CichlidFish.com - Fish That Think.

Thank you for the advice.  I see water changes is the answer to keeping the nitrite/nitrate low.  Good to know how low to keep it - wasn't sure.  I'm going to try the earth worms tomorrow.  Any special kind?  Live-Frozen-Whole-Chopped?  How Much?  I will get a new 100+ tank as soon as he is cured.

When I posted last I didn't realize Rocky's keepers tank wasn't cycled. blueeshomaru17's posts are excellent advice to follow. However I will run over what we in fish keeping call cycling a tank. As blue mentioned, clean looking water is not always clean. At least not for a fish.
Ok here is the cycle: In a new aquarium, the water has little to no "nitrifying bacteria". The reason, there is no food for them. In the first stage, once fish have been introduced, they(the fish)begin to add ammonia to the water. This comes from food waste, fish urine, fish poop, even from gill action (or so I have been told, but not yet really believe it). Now ammonia is very toxic  for a fish. Now the few nitrifying bacteria, in the water now have a food source, the ammonia. As the ammonia builds up, so does the bacteria.
Yet as in all closed loop systems, there is not a quick end. These particular bacteria, that live on ammonia, create another nitrogen component, nitrite, which again is toxic to fish. (not as bad as ammonia, but still pretty leathal).
So another bacteria starts to thrive in the tank, which of course feed on nitrite, and as before, they give off another semi toxic nitrogen compound, nitrate. Now in nature, nitrate is removed by plants, however, in an aquarium, (Oscars love plants BTW, so if your into frustration, try growing some with Oscars) we don't have plants, (you need a lot) so we have to remove the nitrate, by water changes.
Unfortunately, a cycle isn't established over night, the first bacterial colony must grow to a size that it can consume the ammonia before it gets into the water. ( were talking on a molecular level) This takes about 7 to 15 days in most tanks. Then the second colony of bacteria must grow large enough to eliminate the nitrites. Again about 7 to 15 days after the ammonia is no longer readable on the test kits.
Blue mentioned test kits, while I would not recommend a Master kit, this contains tests for ammonia, nitrite, nitrate, Ph, gh kh, potassium, etc. I would just get a kit for ammonia, nitrite, and nitrate. Oscars are pretty hardy and can live in Ph water from 6.2 to 8.5. Its more important for Ph to be stable, than what the actual reading is. The larger the tank, the less swings in Ph, ammonia nitrite nitrates etc. If Rockies still in the ten gallon tank, get him out, even a 20 or 30 gallon tank is better. I will stop now, and post later on how to keep your established nitrofying bacteria colonies healthy in another post. If you have any question about establishing your tanks cycle, just ask.