Maybe try a diluted pedialyte soak. If you do, use only the clear type. Mix 1 part pedialyte to 10 parts slightly warm dechlorinated water and set him in the water bowl with enough to cover his bottom, for about 15 to 20 minutes. It will give him nutrients and vitamins he's been lacking from not eating. You can also try gently force feeding with calcium/vita D3 dusted cricket, worm, etc.

Was the tap water dechlorinated?