Have you ever wondered if digital pool photometers are
accurate? It is hard to compare them to a reagent drop test or test strips and
the only real way to test if they are accurate is to put them up against
another photometer. I had just the opportunity to test their accuracy when I
was able to use five PoolLab 1.0 photometers and my eXact iDip
Photometer/Digital Tester.
Keep in mind this wasn’t done in a laboratory and I
tried to get the exact same amount of sample water in each photometer, but
there is a slight margin of error in this type of experiment. Even so, all of
the test results from the testing were right in line with each other. This goes
to show how accurate photometer testing really is.
Here is how a photometer works:
“Most photometers detect the light with
photoresistors, photodiodes or photomultipliers. To analyze the light, the
photometer may measure the light after it has passed through a filter or
through a monochromator for determination at defined wavelengths or for
analysis of the spectral distribution of the light.” -Wikipedia
The water sample in blanked or zeroed out so that the
photometer tester gets an accurate reading on the state of the water sample
before the reagent is introduced. Once the reagent is put in the water sample,
the photometer tester will read the color change of the water sample. For
example in the pH testing, the lighter the color the lower the pH, just like in
a reagent test kit or the tabs on a test strip. The darker the color the higher the
pH. The thing about the digital photometer is that it will read the color
exactly and give you a digital readout of what the pH is based on the color
spectrum. This eliminates user error and the need to guess at what color the
reagent is.
The first test was for the pH. I used the same exact
water sample in each PoolLab 1.0 and the eXact pH+ Digital Tester. The results
were all within 00.10 of each other.
eXact pH + = 7.73
PoolLab 1.0 Unit 1 = 7.73
PoolLab 1.0 Unit 2 = 7.67
PoolLab 1.0 Unit 3 = 7.63
PoolLab 1.0 Unit 4 = 7.63
PoolLab 1.0 Unit 5 = 7.59
Interesting how the pH was dropping slightly over
time. Between the first test and the last test, about 5 minutes had elapsed. I
did press the wrong button on the PoolLab 1.0 Unit 3 and had to reset it so
that delayed things a bit. I was more careful about the Alkalinity test that I did next so that wouldn’t happen again. But
you can see with even factoring in that the 10 ML sample may not have been
exactly precise in each PoolLab 1.0 Unit, the results were all within the range of
each other.
The PoolLab 1.0 uses a pre-measured tablet that you
simply break up in the photometer chamber. This releases the reagent. The eXact
pH+ uses a probe that measures the pH in the sample and no regent is needed.
Digital Testers are extremely accurate within +/- 0.1% so I was sure that the
pH was 7.73 in this test.
Here are the results for the Alkalinity test with five
PoolLab 1.0 and the eXact iDip photometer. The eXact iDip uses a pre-measured
test strip vs the tablets of the PoolLab 1.0.
eXact iDip Photometer = 146 ppm
PoolLab 1.0 Unit 1 = 156
PoolLab 1.0 Unit 2 = 153
PoolLab 1.0 Unit 3 = 146
PoolLab 1.0 Unit 4 = 147
PoolLab 1.0 Unit 5 = 149
The average between the 6 testers is 149 ppm and this
is within the margin of error for the Alkalinity test. Basically, 4 of the 6 results were right
in line with each other with one being 10 ppm over the others. This can be
accounted for if the water sample wasn’t exactly 10 ML in one of the units. The
pre-measured tablets all came from the same package so the only real variable
is the 10 ML water sample.
These results show that using a digital photometer for
your pool and spa water testing is very accurate. If you used the correct water
sample volume and the correct reagent amount, the test can be relied on
accurate.
YouTube Video Index: http://poolmandave.blogspot.com/2014/03/swimming-pool-tips-reviews-how-to-video.html – A
list of all of my videos.
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