Looks like a magnesium deficiency. Add a little calmag or Epsom into the solution
Edit - it certainly looks more indica than sativa also mate. Maybe a seed mix up??
I’ve had some problems with Mg before but it’s always been yellowing between the veins that gives it away. I’ve looked through a few pictures of Mg def and they don’t look like she does exactly… Not sure if that’s what’s up with her but I’ll keep it in mind
Since its older growth I’d not personally chase it to much but if the newer growth shows similar symptoms something is definitely being locked out. As @ReikoX suggested start with your pH meter.
Did a two point calibration to make sure but the meter was good at both points. I’m pretty religious about keeping my meter calibrated, clean and stored in solution.
pH has been harder to stabilize as it’s been rising but recently it’s not bad. Yesterday was 5.9, today it’s 6.1. I did a reading before and after calibration and was same.
Pretty weird… If it continues another 10 days I’ll probably cull the plant. Conditions are as close to perfect as I can get them so if she can’t hang them she’s gotta go…
Temps and RH are solid, pH is good, EC maybe a little high but no signs of toxicity.
It’s more guesswork from me (no hydro experience) but I’d say due to it being less severe? or new? (IME) It seems like burned leaf material progresses or “heals”. Like a small droplet can become a lens & create sunburn that in no way affects the overall leaf. Both light & nutrient “burn” are just that, temperature too high due to internal chemistry or light intensity.
Oh shit well you can crank that up forsure 1.5 atleast id say. Srry i use ppms at that point 900ppm to 1200ppm is fine i like to foliar spray if i see any deficiency. Hows your root ball look?
I’m in the burn camp as well although I would personally apply some kelp in both a foliar spray with a chelating agent such as fulvic acid. Age Old Kelp is really good and so is BioAg FulPower. The kelp will help prevent stress, increase growth, and if we are wrong about it being a burn, it will take care of the deficiency. Hope this helps! Happy new year!!!
I’m in 1 gallon of hydroton and recirculation via top feed so I can’t see the roots but rez temps have been 72 pretty steady and I use Zone to keep things sterile.
I have Floralicious Plus which has humics and kelp, I could try to add it. Not sure how it will react with the Zone but I think it should work Ok. It’s organic but not alive so I don’t think they will interfere with each other.
Wtf
(no hydro experience) but I’d say due to it being less severe? or new? 
(IME) It seems like burned leaf material progresses or “heals”. Like a small droplet can become a lens & create sunburn that in no way affects the overall leaf. Both light & nutrient “burn” are just that, temperature too high due to internal chemistry or light intensity.
