sunshine 4 mix ph

Ok, maybe can get some help here. Been using sunshine 4 mix (only have added perelite) and been using it for a couple weeks. My runoff water no nuets been anywhere from 6.1 to 6.3 using tap water that has a fairly alkaline base point anywhere from 7.7 to 8.1. Gave some of my babies there first shot of nuets (starting to yellow at tips and in between veins) today was still about a 6.8 going in and runoff of 5.2-5.5. My question is should I worry about this or give it a chance to playout.