Don't add the tetracycline med to your tank as it will wipe the bacteria colony out, as you have only one fish in the tank at present, i would get maracyn two.
Maracyn–Two
Manufacturer: Mardel
A broad-spectrum antibiotic for internal or external gram negative bacterial infections which can even be absorbed through the skin. Effective treatment of fin and tail rot, popeye, gill disease, dropsy (swollen body, protruding scales), septicemia (bleeding or red streaks on the body), secondary and internal infections. Effective even when fish won't eat.
Active ingredient: Mincycline hydrochlor.