Flush those ladies, my friend. If the pH is 6.3 IN/ 7.1 OUT that gives you a soil pH of approximately 7.7-7.9. According to the chart below and by the looks of your plants, several nutrients are being locked out. 6.5-6.8 is the ideal soil pH.

For the flush, you'll want to flush with a volume of water equivalent to 3 times the volume of soil in your pot (15 gals in your case). Do this with fresh pH'd water. pH of the flush water should be 5.75 in your case of alkaline pH. To avoid stress, the pH of the flush water shouldn't be any more than 1 point plus/minus the optimal range, which is 6.5-6.8. Be sure to NOT over-flow the pot with flush water; add it a little at a time, at a rate proportional to the run-off coming out the other end. I know, it's time-consuming but flooding the plant will compact your soil and separate the perlite out, which is a pain in the ass.

Hope this helps, keep us updated!
purpleskunk777 Reviewed by purpleskunk777 on . UPDATE...PLANTS STILL YELLOWING Sorry if I double posted...I added this to my last post and think I am causing some confusion, so I posted in a new thread. What is your experience level? NOVICE Your Equipment: .1) Type and wattage of lights. T-5 .2) Distance from tops? 2 IN .3) Reflector type? T-5 SET UP .4) Is there a consistent fresh air supply? NOT AS MUCH AS ID LIKE...CLOSET GROW FOR VEG. DOOR STAYS OPEN ALL DAY .5) Do you have an exhaust fan and a circulation fan? NO EXHAUST, YES CIRCULATING FAN Rating: 5