Looking for any help figuring out this issue. Seems to have happened over the past 3 days.

Could be cal mag or phosphorus deficiency. More details about it's care up to this point would be helpful.

Im leaning twards nute burn. How are you feeding?

Ok, i keep them pretty comfortable @ 65-79 degrees f depending on lights
I use 1 600W led running 12/12, the plants are 5 1/2 months old started flower on 17th of feb

I have been feeding basically once a week (water every other day or if dry) general hydroponic nutes they live in a 4x4 grow tent with humidity @ about 62-75%(I know it's a bit high, been using damprid to bring it down). I have 2 other plants a sativa(tropicana) and another pheno of this blueberry that seem to be doing fine on the same schedule. blue1 is the plant in question. The browning seems to happen in between the veins and is happening at the top of the plant first? Any further discussion would be very welcome.

I have two photos of the plants about 1 1/2 weeks prior, blue1 is the plant in question. BlueBlue#2 is just the sister plant but exhibits no signs of this browning(other than small brown spots since transplant(another question all together).