If the white patches are raised and fuzzy its more likely a fungus. If the patches look more like areas of white skin discoloration, might be Columnaris, an extremely bad bacterial infection.
Fungus usually can be cleared up with clean water and an antiseptic type med like Melafix.
Columnaris, if caught early enough, might be treatable with antibiotics. It is one bad bug. I've only had to deal with Columnaris a couple of times, on just a few fish. I wasn't able to cure it.