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Re: Nitrate test kits
I guess I should mention how the Hach , NI-1, NI-12, and NI-14 test kits
work as there has been some discussion on "reading" the color comparisons.
These kits use a color wheel which is infinitely variable in color from
clear to the darkest color the test will allow. There are no blocks of
color to compare the sample to, although, this is the method by which their
less expensive kit, the "cube" kits, use. Two test tubes are used. Both are
filled with the water to be tested but only one tube gets the reagent
(which causes the color change). Both tubes are then inserted into the
color wheel box side by side. you then look through both tubes toward a
light source via a viewing window in the box and rotate the wheel to obtain
a color match. The test value is then read off of the wheel via an index
window. This method helps cancel any errors due to differences in lighting
as both tubes are affected by the same light in the same way. The blank
sample assures any color in the test water will be accounted for and
effectively canceled out. The variable color wheel prevents having to
choose between standards.
Overall I am very pleased with Hach test kits. They may cost more than the
commonly available kits but you get what you pay for. The point I made
about error in the test was caused by variances in the individual testers
interpretation of the *instructions* to perform the test not in their
ability to read the test results.