That looks like a lack of nitrogen to me. How many teaspoons per gallon are you feeding Grow Big and Tiger Bloom?
If you are 4 going into 5 weeks in flower, and if you followed the fox farms feeding schedule, did you start reducing the amount of Grow Big they get?
I use fox farms and I have found that I need to feed Grow Big (more nitrogen) in the same ratio as Tiger Bloom all the way to the end of week 6.
My formula is 1.5 teaspoons of Grow Big and Tiger Bloom per 2 gallons of water, I use that until the end of week 5, then I switch to 1 teaspoons Grow Big and 2 teaspoons Tiger Bloom, use that until the end of week 7, then drop down to 0.5 teaspoon Grow Big and 1 teaspoons Tiger Bloom for week 8, then finally in week 9 I eliminate the Grow Big and use 1 teaspoons Tiger Bloom.
I also use Big Bloom and cal-mag with every watering, and Sweet and Sticky sugar about twice per week.
Also, I feed every single time I water until the last week when I decide to harvest, then I will feed plain water for a few days.
Believe it or not, the current grow I have going is two plants, both White Widow (some variant) from seed on the same day, I fed both the same nutrients but one plant grew much faster than the other one. I have been feeding/watering the larger plant every 27 hours, the other plant is more normal and only needs food/water every 48 hours. I was nervous feeding and watering every 27 hours, but it worked out and I am nearly ready to harvest.
That is what I found works for me, I hope it helps.
Now, why is your light only at 60%, too hot? They could use more light with more nutes.
Other than the yellow leaves, the plants look great!
Good luck!
