use nothing follow this and they will be gone in three days. First go get yellow sticky paper at the nursery put it up all over the bases with the little sticks. Than this is the important part. Go get some potatoes from the grocery store cut up little two to three inch strips or squares, of course peel the thing first. Put a couple in each plant bed, pot, hydro container whatever. Switch those out every few hours during light time and give them new ones at bed time. The gnats love the potatoes so they lay their larve on there instead of the soil or whatever medium you are using. The yellow sticky stuff will kill the adults and in less than three days they will be gone along with the larve. Check out the potatoe pieces with your scope you will be amazed.