As for all the bad information out there, most of it is written by people who merely think in their head what is appropriate without actually trying to see if it is suitable for hermit crabs. Most people working in pet stores have never had hermit crabs themselves and they have only been trained to take care of mammals, birds and fish (but even still, some of them suck at that).
Take calci-sand for example. A person who has never examined or had hermit crabs before would think "Calcium is essential for their diet, so it can only be a good thing." However, people like us who have been warned by those who have had bad experiences with it know that it solidifies to a cement-like substance that can potentially trap your hermit crabs inside their shells.
Common (rough and chunky) gravel is claimed to be a good substrate because it is mess-free for owners. True, gravel doesn't stick to our hands, but hermit crabs can't make burrows in it to moult and the pieces of gravel may slip inside their shells and puncture their abdomens.
Don't get me started on painted shells either.
