pH measurement accuracy

platon20

Bronze Supporter
Oct 13, 2016
89
DFW/Texas
I've used a regular pH meter and then bought a fancy/better one -- the Apera

I used the controls and I keep the Apera in the recommended storage solution.

When I initially place the probe in the water, the pH comes out at around 7.35

However, if I let it stay in there, it keeps rising, starting from 7.35 and going all the way up to 7.8 over a period of about 5-7 minutes

This probe is brand new and only been used like 5 or 6 times and I already did the recommended prep/control procedures.

What's going on with the pH fluctuating constantly?
 

jimbethesda

Gold Supporter
Jul 2, 2018
268
Austin, TX
I have the same one, and it does the same thing. You just need to wait until the reading is stable. Not sure why it does it. I’v verified it with the drop test and they are always the same.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
11,654
Northern NJ
When you stick a pH meter into the sample water it can have small air bubbles around the probe. Gently shaking the meter in the sample helps get the air bubbles off and the reading to stabilize. You have to leave the pH meter in the sample until the reading stablizes for a valid measurement.
 

platon20

Bronze Supporter
Oct 13, 2016
89
DFW/Texas
OK so I tried an experiment, I put the Apera pH probe in the pool water and let it sit there for awhile.

Here are my readings.

30 seconds: 7.3
45 seconds: 7.4
60 seconds: 7.5
3 mins: 7.65
5 mins: 7.7
10 mins: 7.8

Which reading is accurate?
 

H-12 1/2 Mike

Bronze Supporter
LifeTime Supporter
Apr 14, 2014
145
Highland Village, TX
I have an Apera20 and have the same issue. If you notice the water temperature is also changing at the same time, so I would use the 5 minute sample or let the sample temperature come up to room temp and use that reading. I have found that for me using the ph meter is more accurate than the color matching. My Apera20 readings match the readings I get from my WaterGuru device. Back in the day, our QA lab would always measure samples at room temperature. But that was before temperature compensating ph probes.
 

revitup

Active member
Nov 30, 2019
36
Pawleys Island, SC
Apera has a support site. I've used it and they ansered my question promptly. Suggest you contact them. I think there's a possibility that your device might be defective.
 

jimbethesda

Gold Supporter
Jul 2, 2018
268
Austin, TX
Apera has a support site. I've used it and they ansered my question promptly. Suggest you contact them. I think there's a possibility that your device might be defective.
What was the answer? I clicked on the link and it looks unanswered
 

revitup

Active member
Nov 30, 2019
36
Pawleys Island, SC
They opened a 'ticket' for me and then, after answering my question, closed it. Apparently the ticket is purged afterward, unfortunately.
The answer to the question was yes, calibration with the 4.0 or 10.0 solution is unnecessary for measurement in the 7s/8s. Calibration with the 7.0 solution is good for 7.0+/-2.0.
 
Last edited:

jimbethesda

Gold Supporter
Jul 2, 2018
268
Austin, TX
They opened a 'ticket' for me and then, after answering my question, closed it. Apparently the ticket is purged afterward, unfortunately.
The answer to the question was yes, calibration with the 4.0 or 10.0 solution is unnecessary for measurement in the 7s/8s. Calibration with the 7.0 solution is good for 7.0+/-2.0.
Thanks!