I have a 30 gallon tank with 2 gold fish in it. It has two Penguin Bio-wheel filters on it and a bubbler in the tank. About a month ago I noticed one goldfish was staying at the bottom on the tank a lot. He would eat but then just come back down after a while. So I tested the water and the Nitrites were really high. It turned out that my tap water had nitrites and nitrates in it. I went out and bought a few plants for the tank and the Nitrites are finally at 0 ppm. There only problem I have now is that the Nitrates are still high. They're at 80 ppm. My goldfish is still at the bottom of the tank but still eating. I've done water changes but nothing seems to bring it down. Im using Prime water conditioner.