I try to keep it at 6.0 to 6.2 through the  whole grow in hydro and coco. I have the dosier on the RDWC and it will use a gallon of PH up every grow to keep it at 6.1. The coco res and the Ebb and Flow I have to use a little PH down every grow. I have no idea why the water sitting still goes up and the water moving goes down but I am told its common,