You would be better off getting an actual snake cage or setting up a tub for him. Aquariums are not meant for snakes, they don't hold heat or humidity well and that tank is much larger than he needs. Getting a better setup would help immensely. Heating pads should be underneath and controlled by a thermostat so they don't overheat and burn him. Temps you should check with a heat gun and I keep a digital indoor/outdoor thermometer for quick checks also. Soaking him for a little while in warm water might help the shed issue, using a bigger bowl, misting and a humid hide will help too as long as he's stuck in the fish tank, same with covering part of the lid.