Could have started out as a scratch. I bought a fish like this some time ago, he got the exact same thing. Strarted out as a bump and then it opened and festered and grew some fuzzies on it. I figured it might have been HITH but never really was sure cause HITH doesn't bump up before it makes pits I don't think I treated with salt, frequent water changes and high oxygenation. Cleared up.