Looks like Potassium deficiency.
The dark green starting from the bottom of the plant going up, the burn happening from the edges of the leaf, the time it is at in flower, the amount of K you give is very little for a big plant like that in full flowering and your plant is foxtailing hard to combat heat, look at all those calyxes growing on top of one another (Potassium helps in managing heat so when it is deficient, the plant burns up like that in the spots nearer to the light and creates itself a looser bud structure to feel less hot.)
All these signs point me to K deficiency. No way you are burning this big plant with 600-1k ppm in late flower.
Potassium can be locked out because of too many salts in the soil such as calcium and magnesium (the relationship between, cal, mag and K is very important as they are all positive ions and can lock each other up if not in the right ratio.)
In your case though, I believe you are giving very little K to the plant, it doesn't look quite mature yet and might go on for a little while because of the foxtailing.
Gl
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Show us how it looks like when you are done harvesting it, I am curious to see!
Your bud looks nice to be honest, terpenes might volatilize though if the plant "burns" up too much.
Also, try organic farming if you are in soil... so much better
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(just my opinion of course)
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