A few snails in your Balkonton is not a problem: they eat the dead worms, digest waste. but unfortunately they also eat your plants.
Anti snail tip: wrap some copper wire around the legs of your Balkonton or vegetable garden container. They never get over that. Make sure that the wire is ‘grounded’, so either at the bottom of the leg, or stick it into the bottom of the earth.
Furthermore, you can try to make the environment less pleasant, snails, like ants, do not like coffee grounds and tea leaves.
More tips? Go to the knowledge base