Drop tank temp to 76° (can be raised to 78 after a week)
Increase aeration of tank.
Maintain 1/3 minimum tank salt dose for rest of Hip's life.
Reduce bottom rock/debris to quarter inch except at live plants.
Inspect your hands (fingernail quick and bed, knuckles) for small blisters.
Treat with gram negative antibiotic for 9 days (maracin-2, trisulfa, kanamycin).
Treat ANY other betta who may have come in contact with your tools and hands with a preventative measure such as Furan-2(jungle fungus cure) or appropriate long duration antibiotic.
Internal infections are most often anaerobic and high O2 levels in the water help the fish survive. Often we carry these infections in our fingernail edges or callouses on our hands, they can also come from our mouths and cat's paws. (cat scratch fever, look it up)