six lines may or may not go after them... usually the latter... if your tank permits I would do something a little larger... melararus, coris and most larger wrasses love snails.
Been there. Wrasses are your only help,, but even that is a futile effort as the snails pretty much only come out at night, while the wrasses hide. Keep removing them by hand at night or siphoning them and if you are persistant enough eventually you MIGHT win the battle.