I have a 20 gallon that I had stocked with about 10 Tetras, 2 Rams., and 2 Cory cats. About two months ago I suddenly had an Ick outbreak. Even though I tried everything I could think of all but two of my fish died. I now just have a Black Skirt Tetra and a Cory catfish left. After all the fish deaths I took all rocks out of the tank and did a 50% water change and vacuumed the sand. When I did a nitrate test it was at 80ppm. I waited two weeks and it was still at 80. I did another 50% water change. After a week I did another test and it was still at 80. I did another 50% change and waited a week. Again it was at 80. I don't know what to try at this point to lower the nitrate. I still only have two fish.