leaves yellowing-with form and pics

Soil Grows-

What is your experience level? novice
Your Equipment:
1.) Type and wattage of lights. t-5 with 500 total watts
2.) Distance from tops? 3-4 inches
3.) Reflector type? enclosed
4.) Is there a consistent fresh air supply? yes
5.) Do you have an exhaust fan and a circulation fan? yes

Your medium:
6.) Specific brand and type of soil, farlands 2-mix
7.) Size of container. 3 gallon pots

Your nutrients and water:
8.) Source of water. tap -well water
9.) Method of checking water ph. ph pen
10) Method of adjusting water ph. ph up and down from hydro store
11) Specific brand and N-P-K ratio for each bottle. fox farms
12) Any additives or tea's? molasses and superthrive
13) Are your ph levels stable, or do they fluctuate? stable
14) What is your ingoing water's ph? ...your runoff ph? ingoing with nutes 6.8 out 6.5
15) Do you foliar feed? no

Your growroom:
16) Indoors or outdoors? indoors
17) What size of closet, room or hut? closet
18) What are the temps and humidity levels while lights are on? ...With lights off? lights on; temp 78- humidity 45% lights off; temp 70 -humidity 35%
19) Noticed any insects in the growroom? no bugs

Your strain:
20) What strain are you growing? nirvana ppp
21) From seeds or clones -seeds

plants are 3 weeks into flowering and leaves already turning yellow. Any clues on why?

You need to start giving them nutrients they need when in flower. Get some canna boost and canna pk. Without nutrients the plant will use up the nutrients in the leaves which causes them to yellow.

I follow fox farms feeding schedule so nutes are being used.