ps233 PH results do not match Hanna digital PH tester!

[waterbear]

OK. I tested the PH 7 solution last night. the solution I had was opened about a month ago but sealed and stored in cool dark place. the PH test closest to the color showed PH of 6.8 (but that's the lowest on the scale). I will try a pool store this Saturday.
Regards

Amir

so you are saying the phenol red turned yellow? if so that means the solution is pH 6.8 or lower. Most pH meters are calibrated at pH 4.0, 7.0, and 10.0 and use three calibration standards. I believe your meter is just supposed to be calibrated at 7.0 and 10.0. (correct me if I am wrong on this) Perhaps the standard is mislabled and is really the pH 4.01 or pH 6.86 standard that Hanna supplies.

edit: I just read the manual for the meter online. Is the meter set up for the right calibration buffer set? (pH 7.01 or pH 6.86) This setting is in your setup mode. Hanna uses two different buffer sets. One set has ph 4.01,7.01, and 10.01 buffers and the other 4.01, 6.96, and 9.18 buffers. If the meter is set wrong for your buffers then the results will not be accurate. The default buffer set is the 7.01 set. If your pH 7 buffer tested closer to 6.8 perhaps you have the wrong buffer set and have to change the setting on the meter.