HELP! 3rd Week of flowering, 2 plants wilting, spots on leaves. Happened fast!

I'm at the end of the 3rd week of flowering in a homemade aero system. Everybody was looking really, really happy, then yesterday one of 5 plants started looking a little sad. This morning, 2 plants are really wilting and I found spots on leaves, pics attached.
I flush my reservoir weekly, and just did this morning. Thinking maybe they were looking like they lacked water, I changed out all of the nozzles. My ppm is at 1200 and I keep the ph 5.5 to 5.9, although the ph seems to rise hourly. After the end of the 12 hour sleepy time, the ph has risen to a little over 7.
Humboldt Nutes - Grow, Micro, Bloom, Sea Mag, Ginormous and Flavorful - 1200 PPM
RO water w/8 gal reservoir - add half to a gal a day
LED lights - 250 watts (have heat issues) - 12/12 cycle
Temp in room stays 77-82 with 50-60% humidity
Reservoir temp stays around 77-80
396gmp pump 1 min on/4 off
17 gal tub with 1/2" pvc manifold w/24 nozzles - Drains back into reservoir
I don't believe I have root rot, I mean the roots are a tan color, except the new growth, but not slimy.
My nozzles are spraying, my water is fresh, I can't figure out what happened. Any help would be greatly appreciated. I tried to nute my babies to death at first, but since they have flourished, hell, I already bought canning jars to store my buds! And now, i yi yi, I'm freakin'!
Thanks Rollitup dudes and dudettes!
 

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