It sounds like a parasite to me too, I would suggest that in addition to the water changes you add half a teaspoon of AQ salt per gallon of water to the tank for a week to help kill it off. I don't know of any parasites that can survive salt treatment. If this is a parasite, it seems this is a new infestation and your fish's immune system hasn't been compromised or anything, meaning that with treatment he won't suffer any long-term effects. Parasites in general aren't that harmful if caught early.
If there's no change after a week, let us know - it's possible that it could be something else, it's just that parasites are the most common issue. He also could have damaged a scale, or could have had a tiny cut/injury that scarred over. AQ salt won't hurt in any case.
Last edited by babystarz; 08-28-2012 at 12:02 PM.