Just keep the temp constant, adding salt won't do much. THe main thing that needs to be done is water changes. Change 50% a week (at least once or 2 25%). Make sure that he does that because thats hte biggest problem. Then I would say that if you feed feeder fish to stop because they don;t have much nutritional value. Just feed hikari gold, and keep doing water changes. I would take pics in a month to see how it clears up. Keep track of the progress and if it looks like its not getting better I would suggest soaking the hikari pellets in a vitamin supplement or just some vitamin water or even smearing them with banana, anything to get more nutrients to him.
I would ask February's POTM winner, as he has a lot of info on treating hole in the head for oscars.