Problem with Snails

I have yet been able to get any snails (Turbo or otherwise) to live in my tank. All my water perameters are good except my phosphates, but I think that is because my RO unit is running to fast. Copper level is zero.
I leave the snails in the bag for a full 3-4 hours to acclimate to the tank water temp and then poke a few holes in the bag and allow the rest of the day to acclimate to the water. I put them in the tank and the next morning they are deceased. They simply stay in there shell and never come out.
I have had no problems with my hermit crabs or shrimp.
Any suggestions?

 

Here's a thought or suggestion. When the snails arrive take them out of their bag and put the water and snails in a five gallon bucket. Then put an old airline hose in your tank with a small shutoff valve on it. Use the kind we all had on our freshwater tanks that controlled the bubble maker (remember that) Start siphoning water out of the tank into the five gallon bucket and adjust the valve so that it slowly drips in. After doubling the volume of water and letting them sit in there for about an hour and a half. Pick them up and put them in the tank.
If I buy mine locally, I ususally just float them for a half an hour and them place them in the tank. If I get them shipped in, then I use the method I just described.

Jim