It only takes one snail to reproduce as most of them don't require a mate to reproduce. It's not surprising that one snail can multiply into a dozen. So, here is the thing to do to control snails. Even though they have the advantage of reproducing quickly,and is able to hide, you can still prevent them away from your aquarium.
You can clip a lettuce leaf on the glass before you go to bed. In the morning you will see a bunch of snails feasting on the lettuce, which you can take it away form the tank and dispose of. Although it wont prevent them from your aquarium, you can minimize.
Another way is to snail-fish in your tank, they will eat every snail they can find. Remember to reduce food for fish so there will no left for snails to eat. The less food you give, the fewer snails may be.