Collonista snails are generally considered harmless and reef friendly and are helpful in controlling algae but as you have found out tend to breed like rabbits I lucked out in that my Yellowtail damsel developed a liking for them and only them as I haven't seen any in quite some time.
There are wrasse that will eat them but then they may make meals out of your other snails, crab and shrimp as well. From what I have heard the best way is the old reach in the tank and pick them out with the fingers routine.
__________________
 My aquarium is nothing but a smorgasbord for my cats.....
|