One of my 5 goldfish died last night. I took him out of the tank to be alone because I noticed he was not nearly as active as the others. Also, he had a white fuzzy looking film over him/her. Any ideas on what that could be? Is it a disease? Should I be treating my other fish for something? I noticed my big goldfish was losing some of his scales, but it appears that he is not losing any more now. He may be an older fish too, not sure.
55 gallon tank
5 goldfish (4 now)
2 plecos