heat, humidity or nutes with pics?

Alright, so I got rid of my downy mildew with Serenade but now I've got something else. All of the sudden these spots appeared (and some shriveling at the base of the leaves.) It is on several plants the reason I am only including these one pic is that this plant had no other issues till this morning. It seems to be affecting the most hardy of the plants.

Since the mildew I stopped adding humidity so the rh is between 20-33%. I also have been keeping lights on temps 80-85 and off 70-75. Supposedly the warmer temps keep it from reproducing. Oddly, this latest thing started after I removed the space heater from the closet (did that Friday night) so temps have been a little lower for a couple days. I have them about 4 inches away for 4 24" t5s and started feeding genesis B and 2 at 1/4 tsp per gallon last week. They seemed to be thriving on it for a couple days. The mild mixture instuctions are 1 tsp per gallon and strong is 3.

Should I not be feeding them every watering (even with this weak solution?)

Should I flush and if so can I flush even the ones with moist soil?

As always - thanks for helping a newb

Btw, I started flushing - when in doubt right? And even the yelowist of the runoff was still only 25o ppm. I was getting ready to repot and introduce to the mh's mid week - any thoughts? Once I get them in the tent and in bigger pots my guess is that the rh humidity will raise a little on it's own.

Also, I got decided to try a spray that my neighbor swears by (for his tomatoes) called green light home & garden insect spray. its all organic so I figured what the hell itd be a good preventive the active ingredients are: .32% thyme oil .33 clove oil and .33% seseme oil. It was a few hours later that i noticed the browning.

any ideas? could it be underfeeding?