The leaves have perked back up since I had started...

From what I can tell from the photos it looks like a nitrogen deficiency. You are in the last weeks of flower I don’t really see any reason to increase your nitrogen levels and I would however decrease your daytime air temperature if at all possible. 88°F is pretty high.

add air flow add fan ppm 400to 480 should be good to go ez fix

I don’t see the downward curling of nute stress. Time it looks more like drawstring or a sideways tip curl which would be more consistent with calcium deficiency. If what I’m seeing is correct then I’d up your cal/mag slightly

Burn it, burn it, what to burn from a plant already burned? :) I hope you to like the lyrics because plant are not enjoying at all the burning. Anyway you loose and i believe as I see it that at the end is going to make you feel very happy. A question, you never defoliate the leaves from the bottom and from the insides of the plants?

Depending on how bad you think it is you can flush the excess nutrients out of your growing medium. As it sounds and looks like nutrient burn. Happens from time to time, all about how you recover from it as everyone makes mistakes. Lesson here would be start with less (less than half the recommendation of nutes and slowly build it up) 0.5ml or so at a time until plants need/show signs of wanting more. Less is always more when feeding ;) But like I said, if you wish you could give her a maintenance flush until run off water is clear and free of build up. Then go again. Hope this helps -Flavoursuk

Yellow leaf tips and curling are signs of nutrient burn. 690 is not a high ppm, but autos typically prefer lower nutrient levels. You may want to try backing down on nutes. The damaged leaves will not change but you should stop seeing new leaves affected