Developed by Hermit Crab Specialists, Fluker's Premium Sand Substrate mixture is the perfect blend of sand, coconut fiber, salt and calcium carbonate that ensures a perfect consistency for burrowing crabs. Probiotic is also added to help breakdown organic waste in your pet's enclosure. One very important element in keeping land hermit crabs alive in captivity is to fill your crab's tank with sand deep enough (minimum depth of 3 times the size of their shell) and moist enough (packs well) that your largest crab is able to bury completely to molt successfully.