U Should Add Some Pictures That Would Help ALOT
and ur PH is Fine keep the Ph between 6.0 to 7.0
like u said ur growing in soil right? then 6.8 is just fine.
About Those yellow spot i would like some pic
it could be a few thing nutes burn, heat burn ect ect
how close are the lights to ur plant
did u spray some nute on the leaves?