If you're using RO water, getting a PH reading can be difficult. Haven't used RO personally, but I remember reading lots of stuff talking about since the water is pretty much pure, there is nothing in it for the average meter to read. So the PH up/down might not seem to affect it until there is enough in it to be way overboard. Most I read would add their nutes to the water, then read and adjust the PH level after there is something in the water to work with. :smoking: