Well they used to do the same in my tank....sit on the bottom and not come up until you put food in the tank, then all of a sudden their snouts would pop out of the sand and they would surface...it was the like the dead waking up, freaky sometimes.....but then they would find the food and eat and go back under the sand. As I stated before, I didn't think much of them until I saw them eating my other snails! So off to the refugium they go where they've been doing well for sometime now.