Ok then, do a waterchange as soon as you can. Get his tankmates out of there and let him be in the tank with no one to pick on him. This will help in recovery by reducing his stress and keeping nibblers away! You need to do an 80% waterchange as soon as you can, and every day from now until he is healed. He needs clean water. If you can do large waterchanges EVERY DAY he will have a chance.
Can you do that?
Can you do that?