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(Assuming you mean the bit on her/his forehead), is this quite new or has a lump/growth been steadily growing and now has a sort-of fungus on it?  If so, I'd be inclined to try eSHa 2000 (or an anti-bacterial treatment that treats fungus too).

Hmmm - if that doesn't work, and isolating the fish in a hospital tank for eSHa 2000 treatment isn't an option, then NT Labs' Anti-internal bacteria or Anti-ulcer & finrot might be best.  I've just lost a fish which had an internal growth/ bony scoliosis that burst through the flesh - at that point, an ulcer and accompanying fungus developed.  If yours heads in this same direction, then I'd probably opt for the Anti-ulcer & finrot treatment (or have it to hand for this eventuality).