I purchased 2 lbs of Diatomaceous Earth (food grade) recently from Mary's to help organically kill off an infestation of Fungus Gnats. Day 1 I was killing (by hand) as many as 50 nymphs per day as they would surface in my pots. By day 2 of applying the DE I was down to only 3. Today is day 3 and I haven't seen a Gnat Nymph yet. Very satisfied with this purchase. I was honestly very skeptical this would work, but so far so good. One thing I highly recommend if you have Fungus Gnats is to also spread the DE in the catch tray and cover the holes where the water comes out as this is where they like to hide and reproduce (where you can't see them).