Is there another fish in the tank? Is there a whitish film forming on your fish? There is a disease called Ick that can get into fish tanks, and fortunately there is a solution you can purchase at most pet stores to put in the water and rid it and your fish of Ick. Tathered edges to the fish, and a whitish film like substance are signs of it. If it is Ick, and your fish goes untreated, it will die. Good luck!
