I would clean it up again with H2O2, then start treating with antibiotics if you think it is bacterial. Skip the Mela-Pimafix products. They are OK for minor, surface problems. You want a strong medicine that will enter the fish's system to attack this from the inside.
Update: Going on Day 3 of treatment with API Liquid Fungus cure. The growth has dissolved tremendously.
i havent ruled out using antibiotics as this may be needed if the wound is still infected.
He's the only cory that has let me treat him by sitting in my palm with a q-tip swab. I would do anything to save this guy and thankful he's recovering. The Molly who also has a white spot on his head seems to be doing better as well. i intend to leave them in quarantine for another week and a half to ensure their slime coat and immunity is back up before returning to the community.
Hi City. I had some similar white funk growing on a cory. Read here: I hit it with just about every commercial med product made for fish! And the funk persisted. Ultimately I nailed it with Bactine, after reading that commercial operations use benzalkonium chloride (active ingredient in Bactine) to treat diseases hiding in tenacious slime coats. The dosage/times are listed in that link. Yours seems to be on the mend now, but in case you need it, there it is. Good luck!
Seen four cases in the last three weeks.
Starts on the lower rear of dorsal and spreads.
Planetcatfish x 2 cases and here and I forget where else.
Nearly always bronze or similar corys.
Be interested in a definitive cure.
Isn't that interesting. Mine started on the snout as far as I could tell, but the next spot was certainly the base of the dorsal. Mine was on a C. metae and bronzes on the same system did not get infected. I hit it with gram + and - antibiotics, salt/heat, and naphthoquinones (Kordon Ich Attack). None of that did anything, then I tried benzalkonium. I did 2 or 3 baths, 60 min each, every other day, 2ppm benz alk (= 1.5ml Bactine in 9.5 cups water). I haven't seen any traces of the funk in over a week now.