COCO COIR Potassium deficiency?

[Greenfingersthc]

A quick rundown...
1.2x1.2m tent
400w hps currently
5 inch filter
15 litre fabric pots (60%.30% coco/perlite)

2x royal gorilla (closest plants on pic)
1x Hulkberry (back plant)
Feeding once every 2 days, canna a+b 2.5ml, 2ml rhizo, 2.5ml calmag, 2.5ml cannazym
water is just 2ml rhizo, 2.5ml calmag, recharge
fluctuate the ph between 5.7-6.2
reluctant to flip due to what looks like a potassium deficiency. but running out of vertical space. Noticed 2 weeks ago, progressively working up.
It's late for me but if I've missed any info just ask.
any advice or direction please, thanks guys!

[LemonBud]

Heres a few diagrams to look over.

[GroBuddy]

langbeinite tea diluted to about 200ppms or to like 100ppms if added with other nutrients. Watch plants response may can get away with more ppms. Be careful lagbontite is high in potassium, if you dont give plant enough time to show progression easy to over due. Good luck

I'd brew for about 48hrs. Can also be used in veg for sulfur deficiency @around 100-150 ppms for foliar spray

[3Berries]

I have K deficiency during flower due to low pH issues in one of my current grows. It's in Ocean Forest soil. I use the langbeinite but have found wood ash to be the cure. Unfortunately it's all over the place depending on where the wood was grown and type of wood. I use green ash trees, got plenty as they Asian ash borers when through here a few years ago.

But they do not look like your plants. They have crispy edges on the top leaves.