Massive differences in pH between Taylor K-1000 and Apera PH probe

platon20

Bronze Supporter
Oct 13, 2016
97
DFW/Texas
Taylor K-1000 is always at least 0.5 pH higher than the Apera. I calibrate the Apera every 10 readings.

For example on today's reading Apera was 7.4, Taylor was 8.2

I'm assuming the Apera is more accurate, but is the Taylor test really that bad? That's a massive difference.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
18,064
Northern NJ
What is your FC level?

What calibrating solutions are you using?

How old is your K-1000 reagents?

Have you tested your calibrating solution with the Taylor test?
 

platon20

Bronze Supporter
Oct 13, 2016
97
DFW/Texas
FC level is 4
Water temp is 58
The K 1000 test is about a year old
I calibrated the Apera for 4.0, 7.0, and 10.0 using the supplied reagents that came with the probe
 

platon20

Bronze Supporter
Oct 13, 2016
97
DFW/Texas
Checked the Apera 7.0 calibration solution on the Taylor, and the Taylor looked accurate (between 6.8 and 7.2) Of note, the 7.0 calibration solution is slightly green so I'm not sure if that would affect the test results for Taylor or not since it's a color change based test.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
18,064
Northern NJ
I doubt your tap water is pH 7.0. I trust the chemical test with pH within the 7s.

Is your tap water from municipal supply or well water?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
18,064
Northern NJ
My bet is your tap water is around 7.8. If you search around your water supply has a water quality report posted somewhere with the pH.
 

platon20

Bronze Supporter
Oct 13, 2016
97
DFW/Texas
You didn't mention how old the Apera calibration solutions are. Are they reused?
It's about 8 months old. But the instructions state that you can reuse the solutions. Surely you don't have to buy a new calibation solution every single time you want to calibrate?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
18,064
Northern NJ
It's about 8 months old. But the instructions state that you can reuse the solutions. Surely you don't have to buy a new calibation solution every single time you want to calibrate?
For best results you should. In industrial use calibrating solutions are single use. I think that is your problem. Get fresh calibrating solution.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
18,064
Northern NJ
So every week I have to buy a new bottle of 4.0, 7.0 and 10.0 control solution?
You pour a bit of solution into a test vial for calibration. Discard the solution after use.

Keep the bottle cap tight and at room temperature. Once opened, a buffer with a pH lower than 7 will last around 3-6 months, while a buffer with a pH over 7 will be good for about 1-3 months.

For pool water testing a meter that does single point calibration at pH 7.0 is adequate.

 

H-12 1/2 Mike

Bronze Supporter
LifeTime Supporter
Apr 14, 2014
147
Highland Village, TX
I have an Apera and purchased additional buffer solutions and their sample tray. What I do for calibrations is to pour a small amount of solution ph 7 and ph 10 (2 point calibration) in the tray and after rinsing the probe do my calibrations. I never reuse the buffer solutions because only a small amount is used when using their sample tray. My Apera is very accurate and always use it to verify the drop test. Sometimes a false reading is given by the drop test.
 
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setsailsoon

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TFP Guide
Oct 25, 2015
2,930
Stuart/FL
I've been using a Hanna test probe for over a year. I suspect your test and calibration technique could be the problem. I learned this the hard way. Here's what works for me:
  • Use a small Nalgene-type small container to keep the calibration fluid you use. It lasts about a week for me.
  • Store the probe in liquid storage solution (add to the cap before you put it on)
  • Prior to each use before turning the probe on shake off the storage solution and dip it in the calibration solution. If it reads the calibration solution correctly then remove, shake it off again rinse in sample then test.
  • If the reading of calibration is off by .1 ph units, dump and re-calibrate with fresh solution.
  • Don't let the probe dry out. If that happens place it in storage solution overnight before using.
  • If your probe reading is not stabilizing within a minute or so something is wrong with it.
Storage solution and calibration solutions are buffers so a little of them left on the probe can throw your reading off if you sample size is small. Ideally dip the probe in the pool and swirl it around. I've used this technique reliable for a long time and at first double-checked with my drop test. They always agree.

If you've let the probe dry out too often it can reduce probe life dramatically. This seems to damage the reference probe more than the glass probe. If this has happened some brands allow you to pull it out a bit more. That's mostly why I got my Hanna tester.

I hope this is helpful.

Chris
 

wogster

In The Industry
Apr 30, 2018
153
Toronto, Ontario, Canada
I have an Apera and purchased additional buffer solutions and their sample tray. What I do for calibrations is to pour a small amount of solution ph 7 and ph 10 (2 point calibration) in the tray and after rinsing the probe do my calibrations. I never reuse the buffer solutions because only a small amount is used when using their sample tray. My Apera is very accurate and always use it to verify the drop test. Sometimes a false reading is given by the drop test.
You use the drop test to verify the probe, not the other way around.
 

H-12 1/2 Mike

Bronze Supporter
LifeTime Supporter
Apr 14, 2014
147
Highland Village, TX
Sometimes I will get a reading of 7.2 with the drop test but the ph meter and the WaterGuru read 7.7. I will then do another drop test and the reading with the same water sample will be 7.8.