ps233 PH results do not match Hanna digital PH tester!

[Amir]

One caution: phenol red is NOT stable with chlorine levels above 3 ppm. The phenol red from Taylor, used in the PS200 should be stabilized to 10 - 15 ppm chlorine, but above that will give various false readings.

Ben

Do I read this correctly? you said 3 ppm. I don't have that much because I run very low CYA (20) and the pool is mostly in shade, but most people here run over 5 ppm in chlorine. How then can they test the PH?
I will test the buffer tonight. I bought my PS kit last year (August) and have last years test soloution and also reordered refill for chlorine and PH last month. I will give it another try and will also compare with the pool company. Thanks all.
Amir

[Amir]

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

[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.

[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.