Agree with Hexamita. Melafix will do nothing at all for it (or much else, IMO). Order metronidazole (Flagyl), and keep their water pristine is the best course of action that I've found. Don't run carbon during treatment. Scarring and pits may be permanent but you usually can stop the erosion of flesh. If you can get Flagyl into their food in addition to treating the water, all the better. Folks on Oscar forums give strong medicated baths of it, but I don't know the strengths used.
Nothing good happens fast in an ecosystem.