Is this heat stress?

This is burning from over feeding/nutrient overload, pure and simple.

Thanks for the comments thus far, it is appreciated, the only thing I haven't considered is what about too cold? I'm going to flush today and see what happens but the damage is already done, nearly every leave on the plant is at least 1/3 damaged. Pretty upset about this to be fair, everything was going so well and then all of a sudden everything's going to badly.

Could be lockout and not a lack of, I am seeing "the claw" leaf tips curl down, dark green leaves, shiny leaves. all signs of nitrogen toxicity. Heat stress you will see all the serrated edges curling up( sign of stress in general ) If it go to cold then that could cause it as it gets colder it hinders nutrient uptake. Good luck

Ph fluctuations

There aren't many deficiency that effect the edges of the leaves around the entire leaf like you have in your pic..From what I've experienced lockout is usually yellow around the edges and works it's way in but I could be wrong, hopefully the flush works let me know

Both magnesium and potassium def usually starts in between the veins, rather than at the edges. The reason I am questioning this is that it has happened so very rapdily. Within 48 hours she went from perfect not any signs at all, to almost every leaf on the plant brown at the edges and looking very unhappy. I am going to flush her, the run off PH is a little high. I really hope this is nutrient lock out because there isn't a huge amount I can do about the temps/lights.

Looks as though you might have a bit of a Potassium deficiency • Improper PH range • Nutrient Lockout (flush and reapply nutirents) • Stressful conditions (VPD) Your VPD might be a bit off from what I can see you down load VPD buddy and compare your Temp and RH to the optimal parameters and adjust from there and check your soil ph as well just to be sure if you get them all. dialed in maybe try the solutions below Organic Solutions: • Langbeinite 0-0-22 (Amended in the soil or mixed in while watering) • Kelp Meal • Glacial Rock Dust (Slow release, requires microbial breakdown) • Wood Ash (raises pH, stay vigilant) Inorganic Solutions: • Potassium Sulfate • PK Booster supplements

It COULD be magnesium ... and each plant is it's own individual and can react differently to the same conditions/feed as plants from the same strain purchased from the same source ... you've got to read each plant and listen to what each one says... https://www.growweedeasy.com/cannabis-plant-problems/phosphorus-deficiency https://www.growweedeasy.com/cannabis-plant-problems/magnesium-deficiency https://www.growweedeasy.com/cannabis-plant-problems/heat-light-stress

Hmm. How certain are you? They're all getting the same stuff and it's only this one plant in the last 2 days? I better double check the run off PH.

Has nothing to do with heat... has everything to do with a phosphorus deficiency... adding some mychorrizae and/or some bonemeal will definitely help here since your pH is perfect and it's pretty hard to overwater in coco (two of the major causes for this deficiency).... Good luck!