As far as assassin snails are concerned, I got 11 of them on Thursday of last week. So far, I think they have killed 2 or 3 of the snails that I have put in the tank to feed them. I honestly think the pond snails are going to reproduce faster than the assassins kill them. At first, I was afraid I might run out of feeder snails, but between what I have growing in my 55 and 10, and what I put into the 29 for the assassins, I think I have them covered for about a year or more unless they are still adjusting to the tank. I have seen the assassins cruise right by a group of feeder snails and do absolutely nothing.