Try slowly (like a couple of degrees a day) raising the temp and throwing a tablespoon per 5 gallons of salt in there. Keep that going for 1.5-2 weeks, depending on the results. Then slowly bring the temp back down. I'd say get the temp to about 90, but there'll probably be some conjecture about that. I'd try and remove the other fish if you can, as this will be pretty uncomfortable. Otherwise I'm hearing good things about garlic treatments, where you can soak your food pellets or frozens in garlic extracts (sold by Kent, Seachem, or the local grocery store, make sure it's in water) and feed that to them. I don't know how well it'll work for external parasites, but it's worth a shot.
