Upper leaves browning between veins

[Guccizillaa]

Day 46 flower, problem started maybe a week ago. at first I thought it was just the leaves changing color normally from flowering, but they're crunchy where they are brown.

Any thoughts? All input is appreciated

 

[PadawanWarrior]

What are you feeding them? Looks kinda like Magnesium deficiency to me, but I'm still kinda a newb.

 

[Guccizillaa]

What are you feeding them? Looks kinda like Magnesium deficiency to me, but I'm still kinda a newb.

Technaflora nutrient line, very similar to fox farms' "performance pack"

 

[OkSureWhyNot]

Coco?
I have similar. Midway flower.
I hear call mag common in flower, esp in coco.
So late in flower, I am thinking let it run through though I added cal mag to last few feedings .
Only a few feedings left anyway.