I know it's hard to watch, but try not to take too many drastic actions. If he's eating, breathing normally and not scratching then I would just keep my water in good condition. Double check your water parameters. What are nitrites at? Are you adding any beneficial bacteria such as special blend?
I would also vary his diet. Try some frozen foods as well as some vitamin soaked nori. A varied diet is really important.
Are his eyes swollen, or just cloudy?