Sorry for the delay - I meant to post this right away. Here are some links showing pictures and methods of treatment. You'll see many people have had trouble eliminating these things... some going as far as cutting down and starting over.

Fungus gnats or WINGED ROOT APHIDS??? - International Cannagraphic Magazine Forums

Here's another thread that discusses them as well:

Phylloxera information - aka root mites aka root aphids - International Cannagraphic Magazine Forums