Use paper towels. I would treat any new snakes as if they come with mites and quarantine them as such, and since you are cleaning his cage, using paper towels should help you spot any problems you would otherwise not easily see with substrate. Add a humid box in the meantime if you worry about humidity. I used aspen in tubs and glass tanks, for both humidity and non-humidity required species. But for new snakes, unless it is a shy eater that burrows, I would use paper towels to check for any signs of mites or other illness and then go from there.