Declaring victory in 2 days eh? I think only time will tell. But I would ask this, if it is the pistol shrimp, why are we contemplating adding another known predator of snails, worms, shrimp.... A CBS.. If you do, you better feed him good and regular...
I wouldn't add the CBS period but if I was to add it I'd certainly add more snails first and see if what I think I solved is actually solved.. Snails are cheap to buy and ship.
hermits are better cleaners than snails.. I willingly sacrifice some snails for my hermits.