Hmmm I can't tell what that is but I would remove the substrate ASAP and change it to cypress mulch or coco choir I would also soak all of the decor and stuff in hot water before placing them back in the tank.
Maybe it's more of a personal preference then but if I were in the same position that's just what I would do. I just think that it would be bothering the tortoise if there were a bunch of tiny bugs crawling on them all the time.Nagh. Thats overkill. Most of these “bugs” are benign and really don’t harm anything unless they are stinging & biting your tortoise. A lot if these bugs come n go. Moist warm substrate coupled with food morsels create perfect environments for critters. As long as it’s not a total infestation, personally I wouldnt let it bother me.