Fish diseases
Fungus
Fungus infections are rare in saltwater fish. And because of that I know little about them and how to treat them. My only experience has been with Percula clownfish and false Percula (ocellaris) species.
A fuzzy, grey growth, usually on the body, appears and grows until the fish dies. Anti-fungal treatments are seldom effective in my limited experience. Luckily I've seen only 3 cases in 14 years.