Hello all, I've only been in the fish hobby for just over a year, and I'm lucky enough that this is the first big problem I've encountered. That being said I have no idea really how to help the little guy. About a week ago i noticed one of my Albino Cory's had bloody wounds along his back, and part of his top fin was missing. This is a pic from a week ago. I tested the tank and the parameters were 0 ammonia and nitrites, 5ppm nitrates, and pH is 7.6. I did a large water change anyways just to be safe, and by the next day his wounds were healing. Over the course of this last week, his wounds randomly reopened, but would close by the next day. He has also lost all of his top fin since, except for the boney parts. He still eats well and swims with the other Cory's, so I was just going to see if he would heal on his own. However now, a week later, the boney parts are fuzzy, and this has me really worried now. Here is a pic from today. I tested the water again, and it's the same 0 ammonia and nitrites, 5ppm nitrates, and pH is 7.6. He is in a 20 gallon tank with peaceful fish, sand, and all decor has been pantyhose tested for sharp spots. All help is appreciated. Thank you for your help in advance!