I use powdered limestone, but in block form, not sprinkled over the substrate. My snails love it so much they ignore the cuttle.
I was advised by a horticulturalist that "lime" means something different than "limestone" in landscaping parlance. In this sense, lime is caustic and would kill snails in a very nasty way. He advised me to make doubly sure I was getting limestone and not lime for my snails, and I pass along his advice to everyone else here.