Gnat Off is a soil drench or nutrient tank additive to kill Fungus Gnat or Black Fly larvae(which appear as small white maggots in the root system).The active ingrediant is a bacterium called Bacillus Thuringiensis which kills the larvae by stopping them from feeding. Makes 250ltrs. Ideally Gnat Off should be used with Pest Off at the same time to kill the adults above ground level and therefore prevent new eggs from being layed.