I don't think there's any other way to rid the snails besides manually. (Meaning any other chemical you use won't work instantly, and you'll still see them in pain.)
If you can remove and crush the grown snails, use PP to kill the eggs. It wasn't a fun thing to watch :/ I tried removing the snails first but a few were hiding.
Veyron Sprite Ayala
S.I.P. Okami, Bahari, Lotus, Mercy, Daihatsu, Ascari, Kuraokami, DaBaDee, Zenvo, & Stella <3