Chewin’ the Choya » First large crab questions about his exo

I rescued a crab yesterday from abysmal conditions. He was kept in a slightly larger than normal kritter keeper looking plastic thing. His friend unfortunately was dead but i took the other guy home and hes active and eating fine and has shells on the way but his exoskeleton seems very dry and hard. I dont expect his exo to be soft by any means but i can hear him walking on the smaller empty shells in the tank. Is this normal? And if not what can I do to help the poor guy