Well, I am glad to help if I can.
I did indeed just have to harvest a grow because of a gnat infestation.
Now, as was detailed in my thread, my problem was caused by a soil
change to Patio Plus (that just let all water fall on the floor) and the
fact that my smart pots crammed together.
The fact is that previous to this one, bad, problem, gnats had always
just been around, but never represented a real threat.
As far as the strongest defense, I think that nematodes are a good way to go.
Good luck,
JD