Growstone Gnat Nix! Fungus Gnat Control, 9-Liter The only scientifically-proven, non-toxic fungus gnat control Made from 100% recycled glass University trials have proved Gnat Nix! used as a top dressing creates an effective physical barrier against fungus gnats Prevents adult emergence from hatching larvae and deters females from laying eggs in the growing media Apply 1/2"- 3/4" layer to fully cover the surface in your growing containers, making sure the entire top surfaces of all containers are fully covered