I had a firemouth with hole in the head a few years ago. I was able to stop the hole from growing, but was never able to get him to recover fully, and he ended up dying. The best information that I could come up with is move the fish to a qt tank and star doing daily water changes, most of the information I found did not point to a solid cause (parasite, fungus, bacterial infection) but they all said that its more prevalent in bigger fish living in suboptimal conditions. Whichthe latter I guess is true of any disease, but anyway. I also treated with coppersafe but I don't think it really helped.