Unwritten rule #1 of Cannabis growing:
If one plant in your grow has an imbalance, they all have that same imbalance to some degree. Nutrition is always the answer no one likes.
All of your plants are overloaded with calcium, causing a boron deficiency. Some plants are more calcium tolerant than others. It doesn't mean you should breed for calcium tolerance. The end result of breeding for calcium-toxic fertilizer has been disastrous to the Cannabis gene pool.
Us old timers raised Boron, not calcium, to tune up our plants. That's the big secret. There is no calcium deficiency in Cannabis. Not a thing. Never was. You guys have all locked out boron on a generic level, and proceed to cull the deformed plants that have any original potential left, opting to keep the compliant nutritively-Gmo'ed stuff that turned purple as it's symptom.
I'd much rather see twisted leaves than purple petioles from a calcium poisoning.Cannabis bud has been bred away from cannabis seed oil production,and towards raw sugar production. All to sell pesticides, boosters flushersnand better new more powerful seeds every year.
Unwritten Rule #2 In Cannabis growing: Fix your fukkin calcium toxicity. There are no other rules guidelines or secrets to follow.