Which was near zero? The nitrites should be zero.

To properly acclimate them you need to drip water into there bag or bucket for at least an hour with a drip rate of about 1 drop every 2 seconds or so. I just grabbed some airline tubing and a valve to build my acclamator. If I was doing it again I would find a U shaped ridgid peice to hang off the tank.

You are just unlucky to buy some nearly-dead snails from the LFS.

While that's possible, it's not proabable. The chances of all the critters being near death is unlikely.