in my experience when fish get like this they do not recover. Get him in a small hospital tank and only fill half way. This will help your fish stay upright. If he's not better, metro or any other strong broad spectrum antibiotic may not be a bad idea. I would use rock salt or aquarium salt. Epsom salt is different. Calcium or potasium chloride I believe. Epsom works as laxative but is not good to use as routine salt IMO. I would get him in the smaller tank, half full so he can stay upright, give antibiotics, and do daily water changes and pray for the best. Hope he pulls through for you bud.