Thermo Fisher Scientific C101 Colorimeter - Manual (Page 22)

Measurement: Cyanuric Acid
C401/102 Colorimeter
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To re-calibrate the meter: All instruments are factory calibrated and user
calibration is not recommended. However, if a Cyanuric Acid standard can
be accurately prepared, or measured by a different method or instrument
of higher precision and accuracy, then a Cyanuric Acid standard in the 66-
75 ppm range can be used. Please refer to section 3.3 Cyanuric Acid for
details.
2.5.5 Chemistry
Cyanuric Acid is commonly used to stabilize the chlorine present in
swimming pool water. With correct pool maintenance, Cyanuric Acid
build-up is uncommon; however, if correct maintenance is not carried out,
the levels may build up until potentially harmful.
In the test method, the Cyanuric acid reacts with the sachet reagent, in a
conditioned sample, to produce a suspended turbidity.
The amount of turbidity produced is proportional to the concentration of
Cyanuric Acid. The amount of 525nm light absorbed/scattered by the
turbidity is accurately measured by the meter and then converted into the
Cyanuric Acid concentration.