Can't really tell about the open wound but from what you describe and from your profile, I would veture a guess that this is from high DOC
in the water. It often fuels the growth of bacteria allowing small problems the fish could otherwise fight itself to get out of hand. A few good water changes over the next week using well aged SW
should help immensely. Make sure the foods are soaked in a good marine vitamin like Selcon or Zoecon containing needed lipids and [acronym="Highly Unsaturated Fatty Acid"]HUFA
[/acronym] (or even >>Beta Glucan
In milder cases, improving the feedings and water conditions will allow the fish to fight it without meds. If that does not help or it gets worse, you will need to QT
and treat with a gram negative antibiotic. Maracyn II at double the dose daily for 7 days would work well. Just be sure you do not treat the display.
Be sure there is no aggression from other fish making matters worse.