It's hungry. That plant is using up N too fast. Make sure your runoff pH is not too low, and if you have more than 3 weeks to harvest (looks like it), you can give ONE feeding with a quarter strength grow fert to slow down the yellowing.
What have you been feeding it in the last couple weeks? Just bloom, right? Does that bloom fert show a N number on the label at all, and if so, what?

EDIT- not K, Mg, or Zn def. N and Ca def or lockout. What was the date of your last re-pot?
stinkyattic Reviewed by stinkyattic on . First Time Caller... Hi, Been looking through the curtains at the site for a while, great place, lots of info and finally decided to give it a go. Have a small problem with a couple of our plants, think it could heat stress, maybe a nute deficiency as well and was hoping that someone could help. E-indoor or outdoor Indoor E-soil, soilless, coco, aero, or hydroponic Soil E-specific medium 10L Pots CSL-Soil type/brand Bio Bizz All Mix Rating: 5