I found out today that my fish has popeye, only in one eye his left to be specific. I just changed his water, he lives in a gallon tank, he had a sign in with him but it broke so I didn't put back in. His water temp right now is 81 degrees farenhieght. I have not checked the ph levels or anything like that. I use tetraaqua aqua safe for tap water. I dont have anything in with him at the moment except aquarium rocks at the bottom. Any ideas of how to fix this or anything?