I'm having the same problem with any new snails recently. They just don't last more than a ~2 weeks,
especially the turbos. My current theory is that they are being stung by the random aptasia anemones
I have since I saw it happen once.
I would have thought I was acclimating incorrectly; or it was the crustaceans, but I only have the green bubble
crabs (mitrax sp?); or there is something in my water, but the other gastropod I have - the baby clam (Maxima)
has been doing fine.
Of course, the few older astreas I have are doing fine <knock on wood>.