Help pls

https://420life.com/wp-content/uploads/2021/10/Marijuana-Leaf-Deficiency-Chart-scaled.jpg

If it was K it would have burnt tips. I'd say it more manganese with the black spots. High levels of calcium or iron can cause a problems with manganese uptake.

You need a PK injection. She's in heavy flower. Make sure everything you put in has a similar ph (water + nute feeds needs to be around the same ph level) be sure to be giving calmag as this helps uptake greatly. Don't let your soil dry up. But with this. You are 100% lacking on heavy flowering needs.

Exactly that happened to me when I switch power for 100%, looks plants need more nutrients, but be careful and control EC, checking your runoff, good tip is use RO water better control with nutrients, this what I did with my previous grow and problem been solved.

Could also be slightly missing out on phosphorus aswell. Add some form of quickly avaialable flowering nutrients asap and use CalMag for watering. Good luck!

Potassium deficiency!! Slight magnesium defieciency aswell (yellowing between leaf veins), but the yellowing leafs with brown spots and necrosis are potassium defiency

Looks like magnesium deficiency