I think it is mouth rot. I treated with arethrimycin (sp) for 4 days and it got better, but it wont heal, and is getting worse locally. I have Cephalexin which is another type of antibiotic. can I treat with that? Here is a pic of the fish. the 2nd pic is another fish I put down. The 1st pic is the fish that I still have but its looking alot like the fish in pic2. what can I do to save this guy? Eating is hit and miss, with mostly miss lately. Nitrates are high (40ppm) but cant get them lower. Thanks for any help