If you have hard water or high KH water, your inverts should be fine. If you have soft water or low KH water, you should look look into slowly adjusting your water parameters using natural solutions like cuddlebone, crushed coral, crushed shells, etc.
it's fine, next time leave it in. they will eat the shell and absorb lost calcium. you can dose calcium supplements and iodine to help it maintain a healthy shell and easier molting.
i dont know if anyone experiences this, but when my bamboo molts, she doesnt eat the exo, or maybe eats very little of it. but i always see practically the whole thing in the tank for about a week until the amano's clean it up