Possible cal/mag deficiency...what do you guys think??

Hey whats up everyone?
IM growing some easy ryder and russian rocket fuel autos. Theyre all about 3 weeks into flower and the easy ryders are doing great but the RRF have some curled edges on the top leaves and the middle and bottom fan leaves have yellow and brown spots which are starting to kill the leaves.
Set up:
2-600 watt hps air cooled
lights are 12 inches from tops
temp is 75 day and 70 night
RH is 40% day 50% night
fox farm ocean forest soil
45 days from seed (about 4 weeks into flower)
using 3/4 strength GH micro nutes
ph is at 6.6-6.8
I thought maybe a cal/mag deficiency but before i did anything i wanted to get some other opinions.
Any help or suggestions about what the problem might be would be greatly appreciated.
Thnaks

Also the spots started at the bottom of the plant and began working its way up slowly. The curled tacoing edges are at the tops only and the leaves are brittle.