hi im jessica, and a few months ago i purchased a couple of russian tortoises from the petstore and one one of them has gotten a lot darker since i took him in and has developed a thick layer of what looks like substrate on his neck, but it wont come off. I have them in a large rubbermaid container with 50/50 play sand and coconut coir with a 100w Zoo Med Powersun UV Self-Ballasted Mercury Vapor UVB Lamp. the other tortoise has not had any of these problems, so i was wondering if any one had any ideas of what this is or any advice
heres a picture:
heres a picture: