It's hard to say without a pic....even then, it can be tough.
What are your readings for
ammonia,
nitrite and
nitrate?
If it looks like grains of salt it could be
ICH. You can treat it without meds by slowly raising the temp to about 84F. Leave it there for at least 2 weeks, do water changes and thorough gravel vacs to pic up all the ich spores. Also increase aeration to make up for less oxygen in the warmer water.
If it looks like an injury, keep the water pristine to prevent infection. You can add a few drops of garlic juice to help his immune system. A little extra stress coat and if you have vita-chem, they'll both help him heal.
If it's none of the above, at least you're not medicating for something we're not sure of.
Lets see what other members have to say, hopefully, they'll have a better idea and can give suggestions.