Hi, I recently rescued a Russian tortoise. When I first got him his shell was fine and was healthy. After about a month of having him now I've noticed that his shell has white spots. At first it was just a small spot but it has become larger recently. It feels as if the colored part of his shell chipped off because the white area is a tiny bit lower than the rest of the shell. I was wondering if this is shell rot or something else. Thank you.