could possibly be a parasite my tiger oscar got a few i just did a huge water change put some epsom salt in the water and a macy something tab and he was good to go he is 1ft long so he was a fighter hope this helps!:fish:
By the title I figured that you already knew what it was and was just complaining about it. It's most likely hole-in-the-head disease. This is a fairly common and easily treatable disease.
You can go and buy medication at any local petsmart or petco. You're going to want to find metronidazole. I recall them having medications with pictures of the diseases on the boxes to make it easier as well.