Last week I brought an Apera PH20 digital PH meter for use in a hot tub. After calibrating the unit with PH 7 and PH 4 solutions with no problems I believe it is working fine.
However, when i use it I get a PH of 8.1
I have 3 brands of paper test strips which show the PH to be 6.8, 7.2 or 7.4. The ideal PH is 7.5.
So the test trips say the PH is low while the calibrated PH20 meter shows it is high.
Which do I believe? Is the PH20 not suitable for this application?