View Full Version : ps233 PH results do not match Hanna digital PH tester!
using PS233 I get a PH of 7.5-7.6 but Henna PHep4 shows a ph of 8.I had just did a two point calibration on the meter. Is there a reason for the discrpancy?Thanks
Amir
http://www.hannainst.com/products/testers/testers.cfm?ProdCode=HI%2098127%20-%20HI%2098128
mwsmith2
06-12-2006, 05:09 PM
Color perception, possibly...although that is a pretty big difference in terms of color.
Michael
waterbear
06-13-2006, 12:28 AM
pH meter electrodes do go bad, especially if they have not been stored correctly or allowed to dry out. That could be a possible source of the the problems. The probe could also need cleaning as per the instuction manual. I have had a lot of laboratory experience with pH meters and that would be my guess.
The Hanna unit was purchased 2 months ago, stored in storage solution, soaked in ph 7 for 2 hours before use (when new) and when placed in PH 7 or PH 10 calibration solution shows correct ph number. I work with color as part of my work (garphic design) and if I could not tell the correct color, I would be out of business. I understand it is the tone not the intensity of color - more orange is lower ph, more pink is higher ph. I guess I need another source to check my numbers - maybe a pool company. I check again this morning, the meter shows 7.6 and the drops show ~7.2! Any one lives in near me that can check their tap water so we can have standard? the meter shows 7.7 for the tap water. Regards
Amir
waterbear
06-13-2006, 07:13 PM
Have you tried checking the pH of the pH 7 standard with the drop kit? Might prove enlightening. Phenol red indicator is pretty accurate but I have seen standard solotions that have changed pH. Depends on how they were stored and how fresh they are. I still lean toward the phenol red indicator.
PoolDoc
06-14-2006, 07:22 AM
using PS233 I get a PH of 7.5-7.6 but Henna PHep4 shows a ph of 8.I had just did a two point calibration on the meter. Is there a reason for the discrpancy?Thanks
Amir
http://www.hannainst.com/products/testers/testers.cfm?ProdCode=HI%2098127%20-%20HI%2098128
I've used Hanna products in the past, and have an extremely low opinion of their quality.
If you have a clear buffer that you can calibrate with, test the buffer with both the Hanna & the phenol red.
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
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
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
06-15-2006, 08:39 PM
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.
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
06-16-2006, 01:41 PM
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.