There is no such thing as a snail too large for a DP They will attack any snail irrespective of it's size. The down side of putting big snails in is that they are likely to die a slow death. The DPs will take take chunks out of them until the snails decide to hide and starve inside the shell.... then death DPs don't eat dead snails either. You don't want the dead snails to cause any ammonia spike in your tank.
Best size snails are the baby ones that are smaller than the DP's eyeballs. The DPs will crunch them whole. Slightly larger ones they will suck the whole body out easily. You can start a hatchery with your larger snails. Hopefully by the time you get your DPs, you will have loads of baby snails ready
Best size snails are the baby ones that are smaller than the DP's eyeballs. The DPs will crunch them whole. Slightly larger ones they will suck the whole body out easily. You can start a hatchery with your larger snails. Hopefully by the time you get your DPs, you will have loads of baby snails ready