I just noticed on one of my turtle Squirtle that his shell near the back of his head is a bit caved in. I can only related to an example of a pot hole on a normal street. Everything is smooth except for this little caved area. I was wondering what the problem was. I give them sufficient heat, lighting, food, and clean water. I'm pointing to maybe a calcium dificiency but if anyone could point me in the right direction I would really appreciate it.
thanks in advance.

