So I've gotten my 55 gallon set up with four big 5-6 inch gold fish and four 1/2 -1 inch gold fish. I did a head count when I got back from school today and I couldn't find one. After hunting for it I found it hiding and there is a wound on it's back. It looks like another fish tried to take a bite out of him. Lucky for me I bought a tank divider so I put that up so he can have some space of his own, but he is not looking good. I put some medicine for treating wounds in but I'm not sure that anything will help. The other three fish seem to be doing just fine. Any advice would be great.