I think they look fine for 4 weeks into flower. Personally, if I was worried at that point I would change their chow to what Jangel suggests. I add 1 TBL. Breir Rabbit or Gramdma's Molasses to every gallon of water when not feeding nutes. Feed them plenty to get a good runoff.
The leaves are going to yellow a bit...basically, the plant feels it is dying, therefore pouring everything she's got into her flowering process. That Molasses is a great source of organic cal/mag, plus all kinds of carbs for her. She's love it, and just be sure you give her a good, clean water only flush about 2 weeks before harvest. After that I would feed only plain pH'd water and water/molasses on alternating feedings till harvest.
Might not be the perfect or best way, but it's worked for me in the past just fine..
Gonna be yummy when their done!
ISO
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The Essence of Compassion
"Resolve to be tender with the young, Compassionate with the aged,
Sympathetic with the striving and tolerant of the weak and wrong......
...... because sometime in your life you have been guilty of all of these."