Day 17 bcn critical xxl auto flower leaves going yellow

Day 17 and the leaves on one of my bcn xxl critical auto flowers are going yellow.
Flushed 2 days ago because thought maybe I nuted them to early.
I use a 250w hps light with ballast.
Any ideas?

What medium? What are you pH-ing to? What nutrients have you and will you be using?

Plants look good, so I wouldn't do anything drastic at this time (including flushing or wildly changing nutrient regimen).

It's a little lighter yellow than you can see,
I'm using
CAL MAG, FLORA BLOOM, FLORA GRO, FLORA MICRO.
PH 5.5 - 6.5