40 Days into Flowering, Fan Leaves Browning and Dying

im gonna say you have an iron deficency due to calcium/magnesium inbalance, had exactly the same prob, treated with calmag, plants flourished but the leaves remained damaged. i might be wrong, but whatyou have looks very similar.

Where can I get calmag?

how old is the plant. how big is the pot. might be root bound.

I'm pretty sure its not root bound, as I think one is my main issues has been when to water. I have been watering just about once a week and seems like the bottom is staying a little damp, and I think maybe I don't have enough roots to soak up all the water. I put a few inches of perlite and some river rocks on the bottom to help with drainage.

vein problems, the parts of the plant affected are the veins and the tips, so u need to tell us what nutes u are using, how much u use, and the % of micro nutes that is in the fertilzer.

I am using MG bloom booster 1 tbspn once a few weeks ago and kellogg organic tomato fert 4-6-3 npk once before that since I transplanted them into this container.

read this and anything else you can find from uncle ben.

https://www.rollitup.org/marijuana-plant-problems/158144-never-ending-abuse-phosphorous-bloom.html

I have a 15 gallon tub that I use for regular watering. ( No nutes )

It's in the grow tent and I add water as needed....but I keep goldfish and snails in there. They keep the water at about 6.4 PH ( along with the algae build up ) and my plants just love it..fish poop. algae etc. I still check the PH but I let nature do most of my work...bugs for bug control etc.
Trying to keep it as organic and natural as possible.

I still test PH..nute and regular watering..both incoming and outgoing.

https://www.rollitup.org/marijuana-plant-problems/427557-fox-farm-ocean-forest-soil.html

READ THIS LINK....