Most of us combine gravel cleaning and water changes (so you clean 25% of the substrate and remove 25% of the old water).

If you don't think this is an injury, and it's looking like a pimple (ulcer-- pus and redness), then I would suggest isolation and antibiotic treatment of this fish. Use kanaplex (at 1/2 dosage, but daily) or the combo of Maracyn I and II.

Salt isn't much of a treatment for parasitic diseases on its own. In saltwater tanks, the high level helps to stop parasitic diseases, like ich, from developing. In additive situations in freshwater aquariums, salt is mainly used to help out an antiparasitic drug, like RidIch+, or in situations where nitrItes are being dealt with (salt can stop them from binding to the gills of the fish).

~Ash