@HotRocks - have you seen flukes do this to one eye - with no other evidence on gills, etc - I recently had a fish that developed this very suddenly - at first I thought it was a trauma of some kind. It certainly didnt have flukes..... In the end it was a bacterial infection. But it also went away without any treatment - I couldnt catch it - but buy the time I could it had nearly resolved. I agree with the maracyn