Keep PH at or near 6.3 - 6.5 ....NOTHING more ... Nothing less.
FFOF is prebuffered right out of the bag at 6.3 . FFOF CAN be hot to “ some “ strains right from the start but ..... plants will acclimate to it as long as you don’t overwater or ADD other Nutes.
It will feed adequately for weeks .... you must range the waters ph to the medium you use.
Under blurple you will water less as this type of light does not make plant transpire as quickly as with hps lights and similar.
I would transplant as stated ... for me .... once leaves grow wider than a small container ... time to up pot. Mix more perlite into FFOF to improve drainage and aeration, and you are golden.
One last tip .... always judge a plant under natural light .... blurple can highlight shit that is not there.