I believe that the majority of nerites are wild caught, hence the damages shells. I tend to just drop snails straight in to be honest, they seem to be able to acclimatise themselves somewhat. That method wouldn't do much anyway, if you really want to acclimate it's better done using the drip method.
I didn't do the drip acclimation because my SG seems to have gone down fairly low anyway, around 1.004. Probably a mix of water changes and salt creep. Going to work to bring it back up to around 1.010 over the next week.
Update on the weaker snail: it was moved a short distance. Appears to be outside its shell right now. Here is a picture:
Will keep watching this one closely. If it stops moving for a considerable length of time, will take it out of the tank.
As for the stronger one, I believe it has buried itself within the thread algae so I can't see it at the moment.
This is what the thread algae looks like now: