Mmmm, right now hes in a 2g, right? Sorry that I can't remember! =(
If he is, I'd take him out and place him in a cup or container for a moment, and then thuroughly clean his entire tank (No soap, just hot water on -everything-; the bowl, ornaments, gravel, filter, heater. Let nothing go untouched. Afterwards fill up his freshly cleaned tank with good water, condition, let it sit for a few hours and take the temp after that. If the temps where it needs to be, place him back in there.
If his coloring is draining, and turning grey, it definently might be an actually disease.... Pictures please? =D