My husband has had fish for years and years. Right now we have two very large tanks (I think a 60 gallon and a 75 gallon). Similar things have happened to us over the years. I know there was a time I rescued a fish off the floor and put him back, only to find that the other fish in the tank began to take advantage of his weakened condition and began nibbling on him. Unfortunately they do that sometimes and that may explain his red, raw condition. I was going to suggest contacting your local store and ask them what medicine to put into the tank. He would need to be isolated and treated separately. It sounds like Leslie is going to come through with the answer later on today. Good luck and keep us posted.