How's he doing? When it's obvious sparring injury and not myco or infected; I don't use any salt or medication.(actually haven't used anything besides dewormer for over 10 years) Water changes are your best course of action. Getting the nitrates down under 10ppm and keeping them low while the fish is healing is what I would do. I don't know that nitrates at lower levels directly affect the fish' healing/immune system, but it is an easy way to see you've gotten the dissolved solids/organics/possible infectious pathogens, etc numbers down without fancy equipment. Also, try moving things around in the tank to break up line of sight and swimming, and giving the non dominant fish places to hide out and heal up.
here's a video collage of some of their natural habitat:
here's a video of how territorial and relentless they can be in their natural habitat: