@Will Ferrell hope you don't mind me jumping onto your thread instead of creating my own but i've won my war with the gnats and wanted to share the victory!
i've battled these little suckers for five or six months. i didn't want to just reduce the population, i wanted to eliminate them. i tried gnatrol, DE, sand, drying my girls out, yellow stickies, etc. i use air-pots and all the holes were not helping. an aside: i would not recommend air-pots to grow cannabis because you're going to get bugs during the process and the holes contributed to the infestation IMO. harder to water and get a good soaking to the girls because it leaks out all the top holes so you have to water slowly, but even then there isn't even coverage if you're not careful.
what helped: a member here on RIU (sorry i don't remember who it was) posted in another thread about watering...and what he said clicked with me. i'd been "drying them all out" but because i have girls in various container sizes, some get thirsty before others and i was doing exactly what he said i shouldn't--i was watering everyone when in there even if they didn't quite need it because i didn't want to have to come back in a day or two just to water the one or two girls...once i stopped that practice AND added CB-80 and put tanglefoot on a container that was really infested, the gnats are gone! the CB-80 is a spray for just the adults--kills 'em dead in the air. oh, i also added two rounds of beneficial nematodes too.
the combination of drying out all girls and watering all of them only when they need it along with the nematodes, CB-80 and tanglefoot on the one pot that was infested did the trick.
yahoo!!!!!!!!!!!