LaMotte Pool Manager Water Quality Handbook - Manual (Page 28)

Cyanuric Acid
What is Cyanuric Acid?
Since chlorine in water is rapidly destroyed by direct
sunlight, cyanuric acid is added to increase the overall
time chlorine will remain in the pool. Cyanuric acid is a
chemical that bonds to free available chlorine, enabling
it to sanitize the water while being protected from the
sun.
Cyanuric acid is available in granular or powdered forms
and is usually added through the skimmer. However,
there are “stabilized chlorine” compounds (dichlor and
trichlor) that already include cyanuric acid. These allow
the pool operator to avoid making periodic additions of
cyanuric acid. A considerable majority of home pool
owners now utilize stabilized forms of chlorine in
outdoor pools.
Why do we test Cyanuric Acid?
Like any chemical additive, cyanuric acid must be
periodically checked to determine if the pool contains
sufficient levels. Insufficient levels of cyanuric acid will
not protect the free available chlorine from sunlight.
Most state public health standards dictate that 100 ppm
is the maximum level of cyanuric acid permitted in
swimming pools. While ideal levels are 30-50 ppm, an
upper limit of 100 ppm was established because cyanuric
acid can only be reduced by pool water removal,
replacement, or by “splash-out.” Sometimes very large
amounts of cyanuric acid can build up if stabilized
chlorine compounds are used regularly over long periods
of time.
Public pools can be closed by local health agencies if
they are not maintained below the maximum level.
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