I have a 40 gal and a 75 gal with MTS and Pond/Bladder snails, not sure which. The 40 is fine, no population problems and everyone does what they are supposed to do. The 75 on the other hand is a different story. I have to hunt to find an MTS and may see 1 of the others, but the substrate is littered with empty shells. Both tanks are as the same as can be parameter wise. The only thing I can think of is I had 2 assassin snails in the 75 over a year ago, but after not seeing them for a while I figured they croaked. Maybe they are still alive and feasting on my helpful snails? Is there any way to trap, expose, or find the assassins? Hope everyone had a great Thanksgiving.