sounds like a massive bacterial infection has set in. without photos there is no way to find out, i would highly suggest you borrow a friend's camera or phone and upload a pic or it will be hard to suggest an appropriate course of action (and likely too late).
also sounds like severe ammonia burn, but this can also be the bacterial infection. keep up with the 50%+ water changes every day and keep temp at 82F (not higher). add 1 tbsp salt per 10g water. again pics will help determine if we need to go to antibiotics, etc. hope he pulls through--
--solomon
sorry about that. i just started fish keeping a couple of months back. one of my first fish was a spotted gar. he was soo cool. he would hand feed shrimp and doo tons of other things too. he seemed to have an infection. idk what it was. he turned white. it was more of a silver spot. i put pima fix in the water but it fixed Sh*t. lol. a week later, my bicher caught the same exact thing and died a slow and painful death. this was soo fast spreading. i think about it time to time and thought to myself that maybe the pleco sucked off their slime coat. is this possible? when i saw the silver spot on the gar the pleco would suck on its body. i never thought anything of it excpet my pleco could be ***. lol. i still have the pleco in the same water that these other 2 fish died in. heres the vid that i made to try to show and cure my gar. u will se a silver spot on the left side of the gar, its by its back fin. enjoy. http://www.youtube.com/watch?v=iiCbq2m2zaI