Deficiency? Toxicity?

These 3 are Tropicana cookies by Canuks. They’ve been in veg for a few months but I can’t get rid of this deficiency so that I can finally put them into flower. They are in coco loco. I’m using synthetic nutes and supplementing with Cal Mag. Feeding at 6.6-6.8 pH. Runoff PH is 6.4. I’ve also tried to give bloom booster to see if it would help. I was pretty certain It’s a potassium deficiency, but my ph is fine and I’m adding in enough. So what else could it be?
 

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