What are the humidity levels in your aquarium. You should have a heat source such as a reptile heat mat on the side of his aquarium. The temp should range in his tank from 74-84 degrees. An adult doesn't need to eat more then 2 times a week. He is new so that is my thoughts as to why he isn't eating. He is still adjusting to his new area. Even if the tank is what he came with they are aware of the surroundings outside the tank...smell, lighting etc. So they still need time for adjusting. If all that fails he may have parasites causing him to look thin. A nice trip to a vet who specializes in exotics is the next step if after he settles in and still refuses food. Good luck.