Ok sounds fine but would of rather had a med that covered neg as well as gram positve.
Triple Sulfa Powder
USE: Treatment of gram-negative bacterial infections, fin and tail rot, mouth fungus and collapsed fins, columnaris.
DOSAGE: 1/4 teaspoon per 10 gallons every 24 hours with a 25% water change before each treatment. Treat for a minimum of 10 days.
Found some more info for you.
Good luck bless him.
Triple Sulfa
Manufacturer: Aquarium Pharmaceuticals
A broad spectrum antibacterial medication that treats fungal infections, furunculosis (aeromonas), fin and tail rot, columnaris, body slime/white body and fin blotches, cloudy eyes, molly disease, and bacterial hemorrhagic septicemia.
Active Ingredients: sulfamethazine, sulfacetamide, and sulfathiazole.
If it get any worse get back to the board, look for the sore eating away at the skin at it will devolope into a hole.