>2weeks till harvest. Leaves started falling off. Let it go?

Hello. Ill keep this short. Plants went in ground 12/2/15. Flowered 1-3-16
6plants total 2-hindu kush 4sour strawberry diesel
12-12 from seed
3 gallon. Miracle grow and yard compost.
600 & 400 w HPS
5x5x6 tent
430cfm exhaust.

Carbon ->600->400-20ftduct6in->blower- on 24hrs (vents into house helps heat upstairs)

Roomintake 200cfm on constant when lights on, 15 on 30 off when lights off

Temps. 78-85 lights on 69 off. 34-38%rh
I have a gnat issue. I kept it in check until a few weeks ago. (Don't wanna smoke pesticides) and they kimnda can back with a vengeance

All went good till about a week ago. Leaves just started writhing up and dying. Turning yello , getting black spots, and falling off the second I blow on them. I know its deficiencys, but should I try and correct it, or just let it finish and learn next time

Rootbound most likely to start. HID lighting makes it difficult to see any problems you describe. Are the leaves falling from the older growth or the newer? Or both? I would cut the lights back to the 600 HPS considering the issues.

My grow is a week or two behind yours (12 on 11-jan) and I experienced the same symptoms a week or two ago. I believe there were three possible causes in my case (fungus gnats, high heat, and over watering). I corrected all three and the situation has greatly improved. I'm not seeing any new leaves, but the existing ones are doing okay the flowers have continued to grow.

To deal with the gnats, I modified my auto watering system to release water about 1.5 inches below the surface, covered the tops with DE and then bounce fabric sheets (with weight to keep them blowing away). I'm also blowing a pretty strong fan across the top of the pots. It may sound extreme, but I've not seen a gnat since the change.

Some clarifications, by "covered the tops" I meant the tops of the pots, and DE is Diatomaceous earth.