PH test results in consistency

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rmturner54

rmturner54

0
Jul 6, 2013
596
Waxahachie, Tx.
I been having the following issue for a while. First of all I am very meticulous with my testing. So the issue is when I run the 1st PH test ,lets say for conversation its 7.2
So I test again to verify and its always higher on the 2nd test. All test after the 2nd one are consistent with the 2nd one.
I rinse the vial and fill to the line each time. I even bought new reagent, only to have the same results. So for my PH purposes I test 3 times and then use the consistent number. I even get my sample water from different parts of the pool.
Any great minds out there have any ideas?
 
rmturner54 said:
I been having the following issue for a while. First of all I am very meticulous with my testing. So the issue is when I run the 1st PH test ,lets say for conversation its 7.2
So I test again to verify and its always higher on the 2nd test. All test after the 2nd one are consistent with the 2nd one.
I rinse the vial and fill to the line each time. I even bought new reagent, only to have the same results. So for my PH purposes I test 3 times and then use the consistent number. I even get my sample water from different parts of the pool.
Any great minds out there have any ideas?
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I work as a biologist on research projects. When we sample water in natural water bodies we also take what we call replicates or two samples (sometimes more) from each location because there is always variability in sampling techniques, and we want to see how much. For your method taking from different parts of the pool could cause variability. To be consistent measuring from the same location and the same depth would be the way to keep the numbers as consistent as possible. But I would guess in so much water with gunite walls or if there has been addition of solid chemicals that would affect pH there could be variable pH in the pool. Probably the best place to take the measurement for a good reflection of the entire pool is at the jets, or average your three numbers together.

This is why I like TFP, it scratches my chemistry itch! [emoji4]. I am sure the pool experts will have a more informed response so I hope they chime in!
 
rmturner54 said:
In different locations i should clarify.
I draw 1 same bottle of water and do all my testing from that bottle, weather it be fc, ph ta etc..... Then next time I test I draw from a different location...same results
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How much time between pH tests as the water pH can change with time? Age of testing reagents? The test method of comparing colors is not really super precise so maybe a tenth off this is not too unexpected. Otherwise I just don’t know. I would average your results. So add up all the results and divide by the number of samples to get the closest to the true value. Also mix well the reagent bottle before titration/ adding to sample.
 
rmturner54 said:
Ive doing it this way long enoigh, i almost think this is normal and a habit. I do 3 ph test back to back wo thinking
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Testing more than once is the way to get the most accurate results when precision is difficult as in this case—but I would average the numbers. I will have to see how mine differs. I do mine by color comparison which is kind of subjective. But I don’t have a problem with maintaining good pH numbers with my well water.
 
HiddenRiver said:
Testing more than once is the way to get the most accurate results when precision is difficult as in this case—but I would average the numbers. I will have to see how mine differs. I do mine by color comparison which is kind of subjective. But I don’t have a problem with maintaining good pH numbers with my well water.
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I agree with taking an average. . Thanks.
One would think...here we go thinking?, that the results would be really close to the same from the same sample bottle of water.
 

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every once in awhile i will run multiple concurrent pH tests, never see a variation as broad as that, usually pretty consistent...maybe 7.6 to 7.8. would be interesting to see what happens if you add 1 or 2 drops of the acid demand drops to see if both sample drop the same amount. if you have a correctly calibrated pH meter that would also be an option to see where you are on that range.
 
rmturner54 said:
Yes eveeytime. I just had a thought though...I wonder if a new test vial would help.
I have actually washed it and scrubbed it w hot soap and water.
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rmturner54–Do you always use soap to wash the vial each time? Soap can have lye in it and may contaminate the sample and cause the pH to be higher. If you could just rinse three or four times with your sample water for replicates that might eliminate the possibility of contamination?
 

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