Anyone know the hardness requirements for snails. I've seen anywhere from 6dH to 12 dH. Does this sound right? I got a nerite last weekend. It moved around the day I put in the tank but that's it. Hasn't moved since. It doesn't appear to be dead and the trap door seems hard. This is the second snail I've had. Same problem with the last one. My parameters are all normal and my water hardness is at a 9 so I can't figure out the problem. Are they difficult to keep alive?