Need Help, Pictures included

I am still semi new at this. These ladies are under 1,000 watt HPS bulbs and have a fan blowing on them. They are in a basement and I just realized a week ago that the temperature was getting down to 62 degrees in the middle of the night. I have since purchased a heater that maintains a 69 degree temperature during the night hours. They have been getting fed fox farm nutes and the pH has been at 5.9. I am not sure what the ideal pH is to be using in soil, perhaps i should be going a little higher, to say 6.4-6.5 (on the water i feed them)? Humidity is at around 50%. Temperature during the light hours is 78-80 and I do not use CO2. They are in ocean forest/light warrior mix with about 67% OF and 33% light warrior. They seemed very happy and healthy until about 7-10 days ago. I have searched everywhere but the symptoms my plants have don't seem to be in any of the generic plant problem diagnosis threads.

The strains are White Widow and OG Kush #18. The leaf curling is more prevalent on the OG Kush, but is also on the WW. Any advice on how to fix this would be GREATLY appreciated, my first harvest was small and I don't want the same end result for this (my second attempt). These pictures are from the end of the 5th week of flowering.

They are in 3 gallon Smart Pots, which are pots made of a clothy material so it breathes well. I feed them 2/3 of a gallon of water at a time and give them just plain RO water every other feeding. If i water on a Monday i typically wont water again until Thursday, but sometimes Wed. if the pots feel light when i pick them up.

Looks okay, just stop pushing the nutrient through them, try Just water ph'd.
that soil is superposed to be loaded, Try checking your runoff.

http://www.greenmanspage.com/guides/plant_abuse.html
a okay reference.

I would flush and then give them 1/4 strength big bloom only with the last gallon of flush water. Looks like nute burn and maybe heat stress or light intensitity issue. How far above the cannopy is your HPS? cool temps are not as big of an issue as high temps are. if anything you wil get some sweet color later in flower cause the cool nights. you want your soil ph about 6.4 a digi soil ph meter is a great tool to invest in. Most of the issues on this site are ph/ nute lockout issues that can be easily avoided. Good luck bro
JP-

Read https://www.rollitup.org/subcools-old-school-organics/44686-subcools-super-soil-33.html He lays it all out.

Looks like a nitrogen overdose, with those dark green, clawed leaves. Flush with 6.5 PH'ed water, then switch to a bloom-biased fert.(low N)

Flush until the runoff PH is the same as your pouring in, and if you have a PPM meter, flush it down below 150 PPM. That'll do the trick, you'll be starting with a fresh medium, after it has a few days to dry out and burn up the excess nutes that were leftover. Then, start feeding again. I'd go with 1/2 strength, at first. Then go full strength, next feeding.