Posiden, just to clarify, what do these snails look like? If they are brown, sorta oval shaped like a football, they are the classic "pest snails" aka pond snails (I don't know the actual species name, have never heard anybody refer to them as anything but pest snails.)
If they are a flat coiled shape, like a rolled sausage or Princess Leia's hairdo in "Star Wars", they might be ramshorns. Those are also classified as pests by some people but others like them and will actually pay (a very small amount of) money for them. These you might want to leave alone as they are more attractive and breed at a much slower pace.
Pest snails are almost impossible to get rid of completely. Best thing to do is just squish them against the wall of the tank and either take them out or leave them for fish to eat. My female Endlers love them and rush over to get them every time they see my finger reach into the tank.
Their shells are very flimsy so just a slight squeeze will cause them to go smush.
Yes assassin snails will get rid of the pest snails but this is of limited help if the problem is you just don't like snails in the first place. I suppose you could get one, let it clean out your current infestation, and then resell it to somebody else for the same purpose.
