Yellowing

It looks like a micro deficiency. Could be any of them, but I think sulfur is most likely. Assuming the yellowing started toward the top of the plant, I'm gonna go ahead and say that this is almost a guarantee. Add some epsom salts to your feed. A tablespoon per gallon should fix her up. Cheers!

Yellowing of leaves is caused by a nitrogen deficiency. This can be caused by incorrect pH, pH of your feed water should be 6-7 for soil and 5.5-6.5 for coco/hydro. If the pH at the roots is not correct you can lockout the plant from uptaking certain nutrients. However, your plant does look a little droopy which can be caused by overwatering. Overwatering can also cause unusual deficiencies even if the pH is spot on. Soil should be dry top 1-2" inches before watering again. In my experience this was every couple/few days with soil. I measure my nutrients by ppm so I am not sure what your mix of nutes equate to. If your soil is becoming dry before watering again, you could try to raise your ppm a little. But I agree, this yellowing is wuite early for the flower process. Goodluck man!