What is this deficiency?

Think it's a little nute burn and PH problem

 

I'd try flushing your plant if you're growing in Coco coir they like a lower pH then soil also btw

 

What the run off pH coming out at?

 

Your coco coir will need the same pH as a hydro set up I normally start out in Coco coir then transplant into some fox farm ocean forest once I have a good root structure I prefer growing in soil personally tho all up to you

 

Being root bound is almost impossible. I’ve had 3 ft plants in 1 gallon pots and they donok
Your problem is that you’re killing them with way too many nutrients. You have nutrient burn all over the plants, you can see the necrotic edges on the leaves.
There is no deficiency, you’re adding way too much fertilizer and you’re probably watering and feeding too often

 

pH my guess

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This is not a deficiency this is major nutrient burn. You are feeding way too much and too often. You should be on a water-water-water-feed schedule. Forget about PH because you’re in soil, anywhere from 5-7 your plant will get the nutrients it needs. Also don’t water so often, let the souls dry.
Get a PPM meter and never feed more ppm than your amount of watts in light. So when you feed, if you have 200 watts on, don’t let ppm exceed 200. And like I said, w-w-w-f-w-w-w-f
Most people water too much, feed too much. Plants need minimal amounts of nutrients. Do not follow the schedule on the bottles.

 

Lockout from earlier pH issues. Correct and give them some Cal mag too

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Lots of people telling you too many nutrients man. I hope you dont feed the 20-20-20 again. Just water next time

 

Potassium deficiency my friend.
Either locked out by excess salt build, or not feeding enough "K".

Reference pic's of plant's with a Potassium deficiency,