Oh. These people think the white poo/starvation syndrome can be cured. How cute. Go ahead. Hit him with metro, prazi and clout. Drown him in formeldahyde, salt and any combination of temperature and nutrient dosing you like. It's kind of a game to see how much money you will blow trying to save the fish.
Your GT will begin to shrink. At first he will refuse all food and seem to be heading straight for the grave. Then, after a few weeks, he will eat something to provide you with false hope. Then, after months and months of starving and shrinking, you'll either euthanize him in pity or he will die. That is the joy of keeping GT's. Welcome to the club.
P.S. Mine liked earthworms for awhile. Of course, he eventually gave up those too and lived on a steady diet of nothing.