I own 4 hermit crabs and 3 of them act "normal" according to what I have read about them. Digging, climbing, snacking, exploring, and resting. I recently purchased the largest one I own and he immediately changed shells several times till he was happy with one. Once he settled in his shell he went straight to the salt water and never left for a few weeks. He hangs half way out of his shell and submerges most of himself in the water. Why is he doing this? Is it normal? Should I worry?