No i haven't treated him with anything other than some stress guard when we moved the tank and all the fish to ease the stress level on them, he's been in this tank for a year or so, i brought the tank from a friend and we moved it.
ill look into that stuff you mentioned, are you suggesting its possible the fish has some form of intestinal worm or something preventing him from gaining some weight? his color is excellent and he's very active, eats voraciously.