I can think of three strong possibilities...
Possible overwatering.
Possibly rootbound.
Possibly just needs to recover from the flush. I've used Fox Farms products for the past few years, and give a good flush monthly to alleviate the salt build-up that Fox Farms is notorious for. Sometimes the additional (prolonged) moisture in the soil stresses the ladies a bit.

Will be a couple of weeks for all the nitrogen in the soil gets used-up from your last application. Once used-up, fan leaves will start to yellow, as the plant scavenges those leaves for it's nitrogen.

oops...I just noticed...you said soil ph is 6.5...? Are you using one of those soil ph probes that are notoriously inaccurate? Can you ph ingoing and run-off ph?

Any other additives, like molasses, micronutes, Sweet...?