Snails and guppies go together well because their tank requirements are pretty much alike (somewhat hard water, omnivorous diet...). Just keep up the water changes (w/o siphoning too many snails out) and overfeed the guppies. :)

I have some tanks with an R.O. mix for breeding selected killies. There is less mineral in the water. The snails' shells get thinner and thinner, actually dissolving! In time they disappear.

One actually could peddle plants from those tanks as snail free. That is a big deal to a few people breeding egglayers.

As with Guppy Girl's clown loach tank, the younger snails are more at risk. Long term, if someone wanted to get rid of all the snails in an aquarium, they could just keep the water soft or loaches in residence and eventually the tough older snails would die of old age but without issue.