Fish has heavy mucus around face which may be brooklynella or bacterial issue
Being a delicate fish, I would remove copper for now and switch to ruby rally pro
Quick cure would work also but rally is milder
Copper itself won't cause that issue. What other fish are in with it? Sometimes, moving fish to a treatment tank changes the dynamics of how fish get along, and there may be fighting. Also, the water looks a bit turbid, or is that just a function of the photograph?