Retreat daily with epsom. You can bump it up to 2 tsp/gal after another day of just 1 tsp/gal (Want to give it its time to work). You can safely go to a max of 3 tsp/gal if you think he needs it. Change out as much water as you can and then redo the salt. 100% change is preferred but sometimes it's not possible.
Wash your hands very thoroughly under hot water before and after handling anything that has to do with him. Try not to mix any of your regular supplies with his since you don't want to spread whatever it is he has to any of your other tanks.
I still suggest a parasite treatment. some of the medication that is in it might do him some good even if it is a bacterial issue. I suggest either General Cure or Jungle brand (I'm US based so unsure on other meds for different areas).
If you don't feel like the parasite treatment is necessary then maybe try an anti-bacterial treatment with Tetracycline or other wide-based medication. There's Triple-Sulfa and Erythromycin based medications too that might be of some help.