What are the water parameters?
What size tank?
And any other tank mates than the Zebra snail?
Has the tank been cycled (takes around 4-8 weeks) builds a beneficial bacteria colony / "BB" in the filter media.
My snails love a good water change.
How often do you do water changes, and how much water?
New to FW fish? First tank in a long time or EVER??? Need some info on keeping fish?
Start here - Aquarium Advice Article
FW Favorites right now Clown Loaches, any shrimp - SW Vase Red Mangroves