So started nutes on my babies today

Plants are just into 4th week… so started with 1/4 dose of fox farm grow big and a little silica. (Soil is ffof) Mixture ph at 6.5… checked the run off and it was at 5.0. Got some dolomite lime to ph up… but should I flush and ph up now or wait till next watering?? Theyre so happy just don’t want to mess it up.