Hi there. What you are describing are definite signs of septicemia in a fish, that means that he does have some sort of infection or build up of toxins within his body.
Its good that he's eating and drinking, and the fact that you have added the bacteria and disease safe will increase the oxygenation within the water to give him the best chance of recovery.
All i would advise for now is to monitor, make sure the water quality remains goo, and perhaps repeat the treatment of the water in a week or so, to keep the oxygen levels within the water as high a possible.
Andrea
Veterinarian
bvm&s mrcvs 15 years as a companion animal veterinarian