I used a wormer called Flubenol-15, active ingriedient Flubendazole, I think.
Add the powder to your tank over a few days and weeks, and all the snails just die. Harmless to fish, but kills invertebrates.
I don't know if it still available or not, but I have Kusuri Wormer Plus at the moment, though I haven't used it on snails.
Alternatively, sterilise the plants before adding them. I dip mine for a few minutes in a weak bleach solution, then rinse them afterwards and soak them in dechlorinator. Not recommended for sensitive plants!
Anyway, this is meant to about keeping invertebrates. I've got Madagascan Hissing Cockroaches.