Just out of curiosity, how many assassin snails did you have, and how many MTS did you add? I added five MTS to my tank for the same reasons you tried, and mine seemed to explode in population in no time at all. I didn't have any assassins though. The three I introduced to a tank with tons of pest ramshorns and bladder snails died pretty fast. I just found their shells within a few months, but the pest snails and the MTS I added long after the assassins had perished didn't seem to get knocked back at all. I might try getting some assassins again at some point, just see whether there can be a balance to have both in the little ecosystem.
