I have 2 goldfish, I've had goldfish since I was a child, but I don't know much about them at all. I know I have to feed my fish and keep my filter running. A few days ago my filter stopped running. The water got pretty bad before I could get it functioning again and there was some black gunk in the corners of the tank. I cleaned my tank immediately, but one of my fish has black stuff lining his mouth, eyes and some on his fins. He seems sluggish. What do I need to do to get him clean and healthy? Please post here or email me at as soon as possible.