I;m a little confused. Is there a differene between molting and changing it's shell. What exactly is the difference and if my crab doesnt change it's shell how do i know if it's because he doesnt like the shells I have or just doesnt want to? Also if it does change shells while I'm not home, wont all the sand that gets in the extra shell bother them? I rinse off the extra shells every day when I change the food & water, but they still get really sandy.