Turbo Snails...eaten or dieing?

I have bought probably 12 big turbo snails in the past month and i only have like 3 left and a tank with dead shells.

why is this? are they being eaten or just dieing?

in the tank there are:
2 tomato clowns
picasso trigger
yellow tang
hipo tang
5 line wrasse
3 cleaner shrimp
1 cow fish
2 peperment shrimp
1 starfish

 

My shrimp took out alot of my snails...

 

food for cleaner, pepermint shrimp and the wrong snails for a reef tank.

 

what snails are good for a reef tank?

 

oh id imagine your trigger has had a good munch too - my lfs does not recommend any inverts with triggers. I personally wouldnt put any inverts in a tank with fish that have teeth

 

Triggerfish could be the culpirt. Also you may not have enough food for the snails! How long has your tank been up?
Usually hermit crabs will impact a snail population as well as they grow and need to replace their smaller shell with a bigger one.