Upper leaves browning between veins

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

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

PadawanWarrior said:

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

Click to expand...

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

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.