fungus gnats

i have a fungus gnat problem and could use some suggestions. im growing in 5 gal homer buckets, two weeks into 12/12. i tried putting 2 inches of sand on top which worked some what, but when then soil/sand dries out it pulls away from the bucket and they get back down there. think some of that landscaper cloth to contol weeds would help? any suggestions? thanks guys, your vast wealth of knowledge is truly a gift.

use coarse sharp sand. peace.

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