I have a bluelabs dual pH and ppm tester. Great tool. Cut to the chase and get a duel unit or wait till you have some extra money and get it then. Like mentioned, your current tester might be ok but check your pen calibration in some 7.0 or 4.0 testing solution to see if is accurate. Calibration is key and most realize it's off after 1 or 2 feeds. If you are adding any ammendments to your water, those can affect the pH as well.
