Help diagnose this problem: Droopy leaves (with Pics)

I'm about 40 days into veg. 4 White widow plants in 5 gal smart post with FFOF. Conditions have been good for most of the grow at about 71-76f at the canopy, 30-40% RH (which I know is fairly low). 10 days ago while I was gone temps briefly hit 84 in the grow room, so I'm wondering if that is part of my problem. The issue is that my leaves are drooping heavily and just looking lifeless. Some of the new growth seems sort of spindly and almost deformed, but not bad and growth has slowed in general. Other than that the plants look healthy, leaves are nice and green.

I'm thinking it looks like over watering or a toxic salt build up. The soil is dry on the top and seems moist but not soaking wet 3" down. I'm just not sure what to do at this point, should I flush with RO water or let the soil really dry out first?

From the looks of it, I'd say they are over watered. I'd let the soil dry out some maybe a couple days and see if they begin to look better or worse. If they start to perk up than it is over watered, If they look about the same or worse than I would flush. What is your PH and PPM/EC from your run off? Have you added anything to the FFOF, like perlite or anything? The 84 F temp would not have hurt them. I don't think that it is salt build up because the leaves look pretty good as far as I can tell and no nute burn. I would go with over watered. If you didn't add perlite, the soil may not be draining that well and retaining to much water causing the over watering problem. I'd go with the ration of 3-1( 3 parts FFOF to 1 part Perlite) Hope this helps and you get those girls looking good!

How long ago did you water? Are you checking ph? Do you have air circulation? Did you say it's dry 3" down? If it's dry that far town she's begging you for water. Plants will wilt when over/underwated.

Heat wont cause droop. If it's to high they will point straight up at the light. I'm gonna say they are very hungry and probably should give them a watering.

Your RH isn't horrible, I've done an entire grow at 25% so I wouldn't worry about that. Just make sure you give them the essentials. Light, H20 ,food, and air. Temps are also ok. That one day at 84 didn't hurt a thing.