one thing too keep in mind with your pH reading is that your pH reading is also effected by a couple other chemistry readings in your tank.
pH, Alk, and calcium all work together. i found out the hard way let me explain.
my tank had a very low pH of 8.0, my calcium was very high (500+ppm) and my Alk(dKH) was very low. so this is what i decided to do. i bought ESV 2 part supplemt. one part is for alk and the other part is for your calcium.
the directions state to add both parts in equal doses. BUT, in my situation i am not able to do that, since my CA is high already. just add the suggested amount of your alk part. testing pH, Alk, and Ca, until your pH and Alk readings are optimal, 8.2 and 8 - 12 dKH. when this rises your CA should drop down to 420ish. now you are in balance and you may add both parts in equal parts. but still keep testing.
HTH