What they've said is true, Emg. I've snails in my 6 gal betta tank, but they are controlled by not over feeding and removing some.
Washing the plants with water won't remove the snails. Plants should really be quarantined, same as fish, because they can carry fish-harming parasites. Here's what I do when I get a new batch of plants in:
3 buckets: 1 with bleach/water, 1 with water, 1 with water and lots of dechlorinator. I dip the plant fully in the bleach water for 10 seconds, then dip in the water and swish *carefully*, then I put it in the water/chlorinator and let it sit until I've dipped all the plants.
Then plants all go into a quarantine tank for at least a week. Nothing in that tank but plants.
Since you've already put the plants in the tank, you could still have more snails on them. If you can: make a solution of about 1 tsp. of alum and 1 quart of water. Remove the plants and put them in the solution. Let them sit for 24 hours. That will kill any snails and their eggs and won't harm the plants.
Alum can be found at the drugstore, or check the baking section of your grocery store. It'll be with the spices as it's used for pickling.
Roan
)