You could try adding epsom salt at 1 tablespoon per ten gallons. It reduces swelling. Don't add it all at once (like maybe 50% one day, and 50% the next), and mix it with water before adding to the tank. Do please provide your ammonia, and nitrate levels. I can't stress the importance of these enough when it comes to determining what's wrong. They are just as important as a photo, if not more. Please provide them so we can get this guy back on the road to health.