It's worth getting a big scale to keep track of his weight, so you can know if he is actually getting skinnier/starving himself to death, or not losing much weight to worry. If his body is no longer a round shape and his spine is obvious, it's also indication that he's underweight.
You can post pictures of him to for people on the forum too, just to see if he is skinny or not.
Thanks for the tip!
He has lived in a glass tank his whole life but I keep it wrapped in paper. I have always fed him in his tank. Feeding boxes don't work for him he doesn't like them. He has also never struck at me or ever shown aggression. He has never tried to bite me ever.