API makes 3 medications (antibiotics) that will treat it. E.m. erythromycin, furan-2, and fin and body cure (doxycycline). It's treatable, and not too late. Make sure the tank he's in stays very clean. Treat for 2 rounds per directions on box. Bettafix and melafix are the same thing. Those 2 and pimafix are more like an antiseptic than a curative. They work great for preventing, but once you see signs it's prob too late for those. On a down note, antibiotics will prob kill your aquarium cycle, so while treating him per the directions, watch your water parameters too.