I think he means the red sore on the jaw, which looks pretty big to me. Possibly an anchor worm or bacterial infection. Like duanes said, clearer pic would help with diagnosis.
In the meantime I would add a little bit of aquarium salt and bump temperature up a few degrees. Also, API "general cure" is a good, mild medicine to use when you aren't sure what something is, it can help with some diseases, parasites, and infections.