Snails very unhappy

[naesco]

Snails require extremely slow acclimatization from the LFS to a reefers tank. Unless you follow that protocol that is the cause of death.

Snails will die if there is salinity changes which may have happened when you changed tanks.

However it is more likely that they are starving to death. Adding ten snails without a reason for adding them and without feeding them is probably your problem.