What deficiency is this?

I think so. I see you have room in the pots for more dirt. I would dump the plant out and put fresh dirt under it. That will buy you a little time. I do it all the time and the plants don’t skip a beat. Chicken manure pellets begin to work in just three waterings. Nice mix of all the main elements, + calcium in high %, and it will begin to burn out around thirty days after it starts to work. Perfect for an auto. I highly recommend you pick some up. Put a few tablespoons mixed in with your fresh dirt if you dump the plants out, and a few more tablespoons scratched Into the soil surface. ( The rate is one tablespoon per gallon of soil)Regular dry food will take too long to work. It’s great stuff, but needs to " cook" before becoming available. Bat guano will also work, but I never saw one with decent K numbers. Like others, I see potassium and calcium issues, but very minor issues if that’s the plant in question in the home depot bucket. I always had problems when I was growing in HD buckets. I don’t know why. Right around the same age the same thing would happen. I switched to fabric and have had much better luck. It’s also a good idea to use an old towel or shirt as not only “mulch”, but also to shade the pot. Cut a slit to the halfway point in the towel or shirt and put it around both sides of the stem, covering your soil, and draped over the sides to cover the bucket. It will keep the sun from cooking your exterior roots, which is where most of your roots are in a bucket. That plastic gets hot.
Good luck, whatever you do.

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