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Re: Hach CO2 test kit

Eric Wahlig said, in part: 

> I also use the Hach CO2 test kit(Cat.No.1436-01). . .it 
> seems that the Low Range
> test(increments of
> 1.25 mg/l) does produce very faint color changes that are
> hard to
> distinguish while the High Range test(increments of 5
> mg/l) produces an
> abrupt and clearly identifiable color change. Most of the
> time I use the
> Mid Range test(increments of 2 mg/l). This provides a
> color change more
> noticeable than the Low Range test and limits the error
> to 2 mg/l. To
> standardize the tests even more, I keep a white piece of
> paper in the test
> kit box that I set the test vial on when I am looking for
> the color change.
> I also try to use the same light source which is easy
> because I run all the
> tests at the same kitchen counter under the same light.
> The test kit is a
> field unit and I have tried to run CO2 tests in the field
> but, because of
> the variability of outdoor light, the Low Range test is
> especially hard to
> read. I have not yet spoken with Hach about this. 

I monkeyed a bit with the same variations and settled on
the mid range test, too, for pretty much the same reasons. 
I still find that I could be off at a minimum of one
titration drop or two, plus any other errors introduced
(too much disturbance of that water, imprecise amount of
sample,) -- the gross margin of error must be at least
about 5 or so ppm.  Good enough for some purposes,
especially when trying to corroborate other methods of
assessing CO2 levels -- if one says about 10 ppm and the
other says about 40, you know you've got problems -- if one
says about 20 and the other says about 15, you're CO2 is
probably about 15-20 ppm.

Scott H.

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