Do you have a glass cover in your tank? Also do you have good water surface movement?
If you have a glass cover, try leaving it open for a few hours and retest. See if it comes up.
Poor gas exchange can drive a PH
down. Here is a test you can do. Get a cup full of tank water, airate it for an hour or 2 and test the PH
. If it is elevated, then you need to get better gas exchange in you system. This can be accomplised by opening or removing part of you glass top and replacing it with eggcrate. At the same time, point a powerhead or 2 towards the surface of the water to agitate the waters surface,this is where the oxygen-carbon dioxide gas exchange takes place
Also may be getting bad readings with the test kit. May want to take a sample to your LFS
to confirm the readings.