Help....ICH? Sick hipo
. If it's ich of course.... Are there holes on the fish or is that an illusion from the picture ? Are what looks like holes only discoloured patches? Maybe keep the 55 as quarantine ... Treat in there ( see stickies on ich) , but a fish this far along will most likely need antibiotics to treat secondary infection.
And set up a proper size tank to keep a tang ... Like a 180 g + and put your inverts in there while you qt and treat your fish ! let it sit in fallow for 72 days + before adding fish from the qt or new .This is extensively discussed on this forum... Do a little reading.
Many people will probably tell you it's too late, but why not try it? At this point what do you have to lose?