"David Young" wrote in message news:zPUhd.346600$MQ5.261894@attbi_s52...
Would it be common for the probe and test kit to be
consistentantly high together? I have checked the calibration of the probe
with 10.0 test solution and it checks O.K. I will locate a new test kit and
check it with that.

Have you used probe to test water taken outside of the tank?
It might be some stray voltage interfering with your probe.
Put enough water into a plastic cup and remeasure pH with a probe.