Thia original gray area has disapeared after 3-4 days.
But now he has a deep area he's gouged out on his head.i don't know how or if there related.

You are making positive progress.. very good. That new mark is a gash from jumping or banging into something. That area almost certain its a tank brace. Your efforts to keep the tank healthy will benefit the healing of that injury. Should disappear in a week, maybe less