Went to the pet store today and asked for some snails for my puffer. Usually they give me rounded snails but today ended up with cone shaped ones. Weren't in the tank for more than 2 minutes and started burrowing in the sand. Is this normal? Concerned because of my salt content (rougly .005-.006) that they are going to die in the sand and affect my water quality.... Is this salt enough to kill them and should I take them out?