As your crabs settle into their new environment, they will periodically molt. Molting involves shedding their old exoskeleton and hardening a new one. Your crabs will grow successively with each molt. Crabs may appear gray of faded before a molt. When a crab molts, it will be vulnerable, as its exoskeleton will be soft and unprotected. It may take a week to more for the exo to fully harden. During this time, crabs may hide for protection. Make sure other crabs are not disturbing them, or it may be best to move them to a secure location. Leave the old exoskeleton in the tank for at least 2 weeks. Most crabs will eat their old exoskeleton to regain calcium and lost minerals. After two weeks, the remains may be removed.