I agree. With past experience give him a fresh water dip daily, and if it's real bad, twice per day. Use the copper or similar treatments and make sure he has a good hiding spot to make him as comfortable as possible. Feed him anything he loves best several times per day.
Do you have a cleaner wrasse or shrimp in the main tank ? As far as I feel, they are invaluable for picking off parasites and dead scales, even inside their gills. On the ocean reefs, most fish go to the end of the reef where wrasse's, shrimp and other cleaners set up a cleaner station, even big groupers and trigger that normally eat them for dinner, will let them be cleaned. The clown trigger will actually turn white and turn sideways, letting the cleaner know he wants attention, then turn back to his normal color and flip his tail saying he's done hen swim away. When we had our 200 gallon, we had the clown and the Hawaiian black stripe cleaner wrasse, and was so cool to watch their daily cleaning job.