First thing.. and this is just me; I would never use a large pot such as the earthbox. I am guessing you put this plant in there from seed and let it go on it's own.

Secondly I would never use a self watering pot such as the earth box; UNLESS I knew I wasn't going to be around very often and even then I would only use the self watering aspect in times that I needed it and hand water the rest of the time.

I am going to guess, despite what your PH reads, that your environment has it's PH gone out of wack.

What method are you using to read the PH of the soil? You are using pro-mix which is peat based soil mix. Peat is acidic by nature and once the dolemite lime is used up in the mixture your soil goes to complete crap.

honestly you need to fill out the troubleshooting form in order for us to give you a more accurate answer; but I believe I'm probably right. Rootbound and PH judging from the pics and symptoms your plants are showing.

Again fill out the troubleshooting form and I'll re-answer.