Problem with leaves

I have a plant that is developing necrotic brown blotches with slight yellowing of the fan leaves. It generally is in the middle of the leaf. The plant is 2 weeks into bloom in FFOF, and the nutes are BC Boost, BC Bloom, AN Awesome Blossoms, Calmag and Humboldt Dark Energy. Total PPM 700 fed every watering. PH is 6.2, temp 86 at canopy, and what might be the problem is the humidity is high at 60-70 (lots of rain in a damp basement), but lot's of air movement. It is in a group of 6 plants close together, but it the only one showing this problem. Any ideas. Thanks

IMO- I think it's a Magnesium deficiency, and Phosphorus deficiency going on at the same time.
It sure looks like both those things.

My problem child just exploded with the same thing. She's been trying to die since breaking soil. I was thinking the same thing, top.