Leaves yellowing and falling off 2 weeks into flowering..HELP

I have two of my ladies headed down the same path. Theyre in MG soil (I know I know) have FFOF waiting for next round.
But on my big girl (blue pot) all the fan leaves yellowed, shrivled up and fell off. I added some epsom salt 3 weeks ago and it seemed to help but now im back to the same prob, but worse.. Now the smaller leaves on the shoots are doing the same. Bud growth still looks good and leaves around bud sites were still nice and green until 3days ago. I flushed then out ph bal water x3 the pot size and added a small amount of cal max
I thought it was a Sulphur def, then read more and it may be an iron or Nitrogen prob. Im lost . Any help would be a life saver. Thanks
a little more info: im running a 400w hps (12-12) following 4 wks on MH for veg. (18/6)
in MG expand & grow soil. LST, 6.5-7 ph
was using dyna grow at a quarter of their reccommended usage per gal and was still getting nute burn so I stopped using nutes probably due to the MG having nutes already present. Tried boosting N a bit, and tried adsing Calmax w no results. The scrawny girl is my problem plant but now my full lush girl which is a month younger from seed is showing signs of chlorosis on lower and mid level leaves. Help please!!

hey shut those hps light off and retake the pics please , very hard to see plant with hps lights. can turn off use the flash on the cam will not hurt any thing, also its not the mg soil, I use that shit as well. and have no problems,

I'm having the same problem under led in soil with 30% perlite my yellowing leaves and even some new growth have dead patches aswell

Photos updated. Blue pot is my oldest plant where most the leaves are falling off. The grey pot is my bushier girl and shes showing signs of yellowing throughout the whole plant, mostly fan leaves at this point within the last 3 days.

No other advice. .. ??? Im loosing a handfull if leaves a day!!

Hey did u figure anything out???