I've noticed that my initial read of pH is coming up low, the color is more yellow and tests about 7.2 - 7.4. I know my pH is not that low, so I retest. Using same water source (I pull water from pool in cup) the 2nd read shows what I expect it to be (7.6 - 7.8, or higher). This does not happen every time, but it has occurred frequently enough that I thought I'd look for reason. At first I thought it may have to do with residue from the chlorine test, but I now rinse and dry the tube after the chlorine test which I would think removes any residual chemicals. Any ideas on why the first reading would be so different/low?
Why Difference in 1st and 2nd pH test?
- Thread starter bobandsherry
- Start date
rajung
Well-known member
Not sure on an answer why, but has happened to me but the opposite.
A few times through out the summer, my PH would show 8 or higher,knowing day before it was 7.4 covered and no pool activity.
Dump sample check and shows 7.4
Get new sample and shows 7.4
always get roughly 16oz in plastic measuring cup at elbow deep depth.
Not sure if at times a little deeper or shallower.
Pretty sure I add correct drops, but is only solution I can think of not correct on the drop numbers.
Sometimes happens on my CYA tests also.
I do the same process if off. from previous test by much.Often wondered the same but never inquired once my tests showed good on 2nd and 3rd tests back to back with new water sample for each.
A few times through out the summer, my PH would show 8 or higher,knowing day before it was 7.4 covered and no pool activity.
Dump sample check and shows 7.4
Get new sample and shows 7.4
always get roughly 16oz in plastic measuring cup at elbow deep depth.
Not sure if at times a little deeper or shallower.
Pretty sure I add correct drops, but is only solution I can think of not correct on the drop numbers.
Sometimes happens on my CYA tests also.
I do the same process if off. from previous test by much.Often wondered the same but never inquired once my tests showed good on 2nd and 3rd tests back to back with new water sample for each.
I rinse everything well after doing my testing, using the pool water to rinse. I also rinse the cap that goes onto the pH tube. Next time I do testing, I first rinse again using the pool water sample before starting the test. I get consistent results.
Oly
Gold Supporter
Yes rising test equipment is important. Best done with distilled water or deionized water. Tap water is better than pool water
rajung
Well-known member
Thanks
I always rinsed with extra pool water sample, figured clean pool water residue next time would dissipate.
As noted in original post, I rinsed and dried tube before testing. Used tap water as well. Perhaps I wiped the cover as well, but perhaps small residue from chlorine test still on the top could alter results?
Oly
Gold Supporter
Right contamination is probably the reason, it is a small sample. How about we pH test the diluted residue after a FC/CC test and find out? If pH is impacted we can isolate the powder and both reagents. So trouble free we are Looking for trouble. 
I rinse with tap water after tests and put it all away wet.
When I go to test next, I always rinse everything with my pool water sample, then do the test. Have not noticed any in consistencies like you mention ... but then again I do not usually do any of the tests twice. Might have to try the pH and see what happens.
When I go to test next, I always rinse everything with my pool water sample, then do the test. Have not noticed any in consistencies like you mention ... but then again I do not usually do any of the tests twice. Might have to try the pH and see what happens.
Oly
Gold Supporter
I had a chance this am to test this theory and not rinsing after the FC test did significantly lower the pH test that followed.
After the FC test I dropped out the 10ml sample, shook out the tube then filled with pool water and tested pH which was 7.2
Rinsed the tube with tap water refilled with pool water and the pH tested 7.6+
Did not test if it was the powder or the reagent that affected the pH but does not matter. You have to rinse between tests for accurate results. I guess it makes sense this is line one in the instructions.
After the FC test I dropped out the 10ml sample, shook out the tube then filled with pool water and tested pH which was 7.2
Rinsed the tube with tap water refilled with pool water and the pH tested 7.6+
Did not test if it was the powder or the reagent that affected the pH but does not matter. You have to rinse between tests for accurate results. I guess it makes sense this is line one in the instructions.
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