dude think about it when you add nutes to water your ph goes down
therefore if your ph rises your plant or plants must be consuming the nutes
if your ph rises your plant or plants are drinking more water than nutes,
if you have the perfect mixture your ph would be more stable.

how big is your resavoir ? a bigger resavoir helped me out but i still adj my ph every 24 hours or so i never would let it get over 6.5 sometimes it would go 2 days without needing adj.

sounds weird but distilled vinegar will bring your ph down i use it and it works great its cheap also


good luck with your grow