Sand can cause impaction in leos, which can kill them. I took them off sand and put them on coco husk. I feed them with tongs now so they don’t eat dirt or sand.
My one gecko Grif, was on the thin side for awhile, even though he ate. I fatten him back up to a more healthy size. Their diet consists of crickets, super worms, wax worms (as a treat, can be used to put weight back on thin geckos), giant mealworms and hornworms. If I can get dubia roaches they will have them to.