LaMotte Pool Manager Water Quality Handbook - Manual (Page 25)

Why do we test Chlorine?
Sanitized water in a public pool is top priority for public
health inspectors. Testing and maintaining an adequate
level of Free Available Chlorine is a daily goal of the
pool manager. Most states require free chlorine levels of
at least 1.0 ppm. Tests should be taken several times a
day, two to three times under normal bather loads, and
more frequently when heavier bather loads are
experienced. Local health departments usually have
requirements for testing frequency.
Testing for chlorine is not limited to measuring Free
Available Chlorine. Regular analyses for the amount of
combined chlorine should be made as well. By testing
combined chlorine once a day or several times a week,
the need for superchlorination can be determined.
Combined chlorine can cause chlorine odor and severe
eye irritation. A combined chlorine test will indicate
that superchlorination is required rather than a simple
pH adjustment. Combined chlorine levels should not
exceed 0.2 ppm.
How do we test Chlorine?
Prior to the introduction of DPD (diethyl-p-phenylene
diamine) in 1969, most chlorinated pools in the United
States were tested with OTO (orthotolidine). OTO is a
colorless liquid that produces a yellow color when it
reacts with chlorine, and as with most colorimetric tests,
the color is proportional to the concentration. Since
the test is not suitable for or measuring the Free
Available Chlorine, its use is not permitted at public
pools in almost every state in the nation. Most state
health codes specify that a test kit must be on site for
measuring Free Available Chlorine, and some even
specify that the kit must use the DPD test.
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