Question: Should I Leave the Molted Exoskelton in the Tank?
Answer: Yes! The molted exoskeleton is a rich source of calcium, which your crabs needs to grow a healthy new exoskeleton. A freshly molted hermit crab will usually munch on the molted exoskelton for the first few days after molting. The other crabs in your tank may also benefit from eating molted exoskeletons. If a crab has molted in an iso tank, once it is safe to move the crab back to the main tank (guidelines can be found here), you can also move the uneated bits of exoskeleton in the main tank for the other crabs.
There will be bits of the exoskelton that are too hard to eat, though, so after a few weeks you may want to remove these bits.
It is also a good idea to provide other calcium-rich foods for your hermit crabs, such as cuttlebone, crushed oyster shell, and crushed boiled egg shells.
Go To Hermit Crab Molting FAQ for more on molting hermit crabs