Ugh. Sorry to revive older thread, but I am suddenly finding a bunch of these annoying little bastards in my tank, too. Look like small bird droppings. I don't want Assassin snails since I have Nerite and Mystery snails that I actually like. Anything work other than constant manual removal? (and the lettuce trick to get more out)
I have been completely unsuccesseful in removing mini-ramshorn without poisoning via copper.
They are the plague. I have had them survive bleach and potassium permanganate dips. I finally got rid of them in a 10g quarantine tank (which I had bleached... wtf), via copper. I haven't tried the H202 method, suggested above, yet. Sounds promising to me though. Either method would requiring removing the snails you wish to keep.
I've scoured the net trying to find a way to get rid of these unsightly bastards. Adding assassin snails does not work. It appears the only way is to remove all the snails and shrimp that you want to keep and then either add aquarium salt or snail be gone. Let me know how it goes. And good luck.