I agree. If yellowing fans are the only problem...it's not really a problem, and it's possible the usable light isn't extending down to the lower branches. How tall are they?

You mention water ph is 7.0, and that you adjust it with baking soda? Is this to adjust the water up to a 7.0? (baking soda raises ph, for those interested)
Pretty much any ph between 6.3 and 6.8 is recommended for peat-based soilless grows. What's the water out of the tap?

Molasses has calcium, magnesium, other micro's and iorn. Helps with late flowering chlorosis, and is the base ingredient of a lot of 'bulking' or 'carbo-load' formula's.

Would let the yellowing leaves fall off on their own, but don't let them accumulate as leaf litter. Bugs reproduce under them.
Rusty Trichome Reviewed by Rusty Trichome on . YELLOWING...DRYING UP FAN LEAVES.... What is your experience level? NEW-B Your Equipment: .1) Type and wattage of lights. 400W HPS .2) Distance from tops? 12-18 INCHES .3) Reflector type? BRIGHT STAR, NO GLASS, NO COOLING .4) Is there a consistent fresh air supply? I BELIEVE SO .5) Do you have an exhaust fan and a circulation fan? YES .6) What are the bulb wattages, kelvin ratings, and schedule? 12/12 Your medium: Rating: 5