ps233 PH results do not match Hanna digital PH tester!

[Amir]

the meter was calibrated at 7 and 10 (the meter shows what buffer to use it was set to 7.01 10.01 and 4.01) I just ordered a new batch of buffers and try again. Could the phenol red that I got last year is bad?

Carl,
was my understanding correct that you can not trust the ph reading above 3 ppm ? is this true of last year PS233 and this year refill of phenol red?
Amir

[waterbear]

was my understanding correct that you can not trust the ph reading above 3 ppm ? is this true of last year PS233 and this year refill of phenol red?
Amir

Phenol red is converted to chloropheol red in the presence of high chlorine levels. Chlorophenol red will test a pH range of 4.8 to 6.6 and displays the same color changes as phenol red in it's range....yellow below 4.8 for chlorophenol red and 6.8 for phenol red, purple abovel 6.8 for chlorophenol red and 8.2 for phenol red. This interferance can be minimized by adding sodium thiosulfate to the indicator and the better quality reagents such as the ones from Taylor Technologies (which is what is in Ben's kit) already include this and are accurate up to 15 ppm chlorine.