I agree with the other posters. If you have had luck getting him to eat and behave normally in a 100 gallon tank, kudos. If not, however, he is likely suffering some anxiety from too much open space.
Also, how are your temps? In a tank that large, are you keeping your ambient and belly temperatures high enough and a decent gradient from "warm" side and "cool" side? What does the rest of the tank set up look like?
If you don't want to put him in smaller tank, you can try crowding the big tank and see if that helps. Lots of boxes, fake or real plants, bits of wood, hides, etc.
Finally, the Ecoearth will dry out eventually. Fluffing it up once or twice a day will speed up the process. If you are worried about him sitting on moist soil all the time, try putting a hide with a bottom in the tank. A tupperware container with a hole cut in the side works well. He can crawl in the tub, feel secure and get his belly up off the wet substrate.
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25 year old 0.1 from Lincoln, NE
Ball Pythons - 0.1 Pastel, 1.0 Pastel het Pied, 0.1 Pied, 0.1 Cinn, 1.0 Black Pewter, 1.0 Woma (hidden gene?), 0.1 Yellowbelly, 2.1 Normals
Kingsnakes - 1.0 L. m. thayeri, 0.1 L. m. thayeri X L. alterna, 1.0 L. g. californiae
Other - 0.1 Whitesided P. catenifer sayi, 1.0 H. nascicus, ?.? Chrysemys picta, 0.1 crazy cat, 1.0 husband