In Part 1, we discussed the importance of maintaining the free
chlorine at or above 1.0 ppm to
prevent infections caused by germs
in the water. However, this is not the
only aspect of the essential testing
needed to properly maintain a body
of water. To ensure that free chlorine
remains effective, the pH must be
monitored and adjusted. Each year,
there are dozens of pH excursions that
lead to chlorine gas releases. Besides
free chlorine, it is essential to monitor
the combined chlorine, as this large
group of halogenated compounds,
also known as disinfection byproducts
(DBPs), are also a major source of
Recreational Water Illnesses (RWIs).
Although there are no available statistics
on the frequency of DBP-caused RWIs,
anecdotal evidence from swimmers
and parents strongly suggest that DBPs
cause more illnesses than germs.
In North America, the standard
operating range for pH is 7.2 to 7.8.
These values are the PHTA standards
which are well established and applied
as best practices. They are included in
many state and local pool regulations.
These limits balance disinfection
efficacy, corrosion control and swimmer
comfort.
The upper limit is based on the
killing efficacy of hypochlorous acid.
As pH rises above 7.5, the reduction
in hypochlorous acid and subsequent
increase in hypochlorite ion results in
less killing power of free chlorine. In
theory, increasing the free chlorine as the
pH rises can maintain the same killing
efficacy. For example, at pH 7.5 and 2.0
ppm free chlorine, there is 1.0 ppm of
hypochlorous acid. To have the same
1.0 ppm of hypochlorous acid at pH 8.1,
you would need 5.2 ppm free chlorine.
However, this example does not account
for the complexities of recreational
water chemistry, including the impact of
cyanuric acid. The simplest approach is
to follow well-established standards and
maintain the pH between 7.2 and 7.8.
Besides, arguing about chemistry with
a health inspector who is about to close
the pool for being outside the legally
prescribed upper limit is not likely to be
an enjoyable encounter.
Elevated levels of combined chlorine
cause rashes and eye irritation that
typically resolve after a few hours
without requiring medical treatment.
There are more than 800 known DBPs
in chlorinated and brominated waters.
Some of these chlorinated compounds
can be detected by standard DPD
pool test kits. At best, the results of a
combined chlorine test are an estimate
of the concentration of DBPs in the
water. OTO pool test kits are no better
and, in another way, much worse in they
only reveal the total chlorine (free plus
combined).
PERSISTENT MYTH
A significant amount of research has
shown that concentrations of combined
chlorine often exceeded 0.4 ppm and
occasionally surpassed 1.0 ppm. After
the change from OTO to DPD test kits in
the late 1960s and early 1970s, there was
a noticeable reduction of rash reports
observed in the scientific literature.
This suggests that a combination of
better testing methods and increased
awareness has reduced the historical
number of rashes from DBPs. However,
one persistent myth in aquatics is that
the smell of poorly managed indoor
pools is due to excessive chlorine. In
reality, the odor comes from several
dozen well-recognized but highly
odiferous volatile DBPs. Poor air quality
indicates that the water contains
excessive concentrations of these volatile
DBPs.
While most illnesses from DBPs
are minor, a limited number of people
develop more severe chronic medical
conditions. Chronic conditions develop over years of repeated exposure and
are generally undocumented in the vast
majority of swimmers. These conditions
can lead to breathing issues and some
investigators suggest this includes
asthma. Several European studies
have shown that there is a correlation
between swimming and asthma. This
suggests that inhaling chlorinated
water vapor while swimming causes
asthma. But epidemiologists say that
correlation does not prove causation. In
simple terms, a higher incidence rate of
asthma among competitive swimmers
compared to non-swimmers is not
considered proof that swimming caused
their asthma. An alternative explanation
is that competitive swimmers may have
different metabolic and immunological
makeup that predisposes them to higher
incidences of asthma. The jury is still
out on the true cause of the association
between swimming and asthma.
There is one category where DBPs
are directly and positively linked with
allergic reactions – severe rashes due
to hypersensitization from repeated
exposure to chlorinated water. Aquatic
physical therapists spend several
hours per day in the pool for years
of their professional practice. In
time, their immune system becomes
hypersensitive to chlorinated, or
brominated, compounds. Even when the
concentration of DBPs is undetectable
by conventional test kits, their immune
system becomes so reactive that any
exposure results in severe rashes. The
only solution is to cease all exposure
to halogenated water. In the case of
this group, it requires a change in
employment to non-aquatic jobs.
BREAKPOINT?
If high combined chlorine is bad, why
not just use breakpoint to control it?
Isn’t breakpoint supposed to eliminate
combined chlorine? NO! Breakpoint
is not designed for swimming pools!
Breakpoint was discovered in the
1930s when drinking water was being
treated with chlorine in combination
with ammonia or an ammonia
compound. Breakpoint chemistry is
optimized to eliminate chlorinated
ammonia compounds (mono-, di-, and
trichloramine). Human perspiration
and urine contain dozens of organic
compounds but only trace amounts
of ammonia. Each one of the organic
ammonia compounds reacts slightly
differently than ammonia during
breakpoint. This means both the
concentration of chlorine needed
and the time required for reaction are
different than with just simple inorganic
ammonia. Since you are not able to
determine the exact composition of
organic compounds present, you can’t
predict the required treatment dose or
time required for a full “breakpoint.” The
net result is that breakpoint in a pool
may eliminate some of the combined
chlorine but not all.
How much combined chlorine is
too much? The ANSI/APSP/ICC-11
2019 American National Standard for
Water Quality in Public Pools and Spas
states 0.4 ppm combined chlorine
is the maximum. Some individuals
are much more sensitive than others.
Further, some DBPs are more irritating
than others, and the 0.4 ppm limit of
combined chlorine may be too high for sensitive individuals. With indoor pools
that have less air exchange, it may be
that very low concentrations of DBPs
will cause objectionable air quality. In
these cases, a systematic approach to
better water quality management and air
exchange are needed.
RASH EFFECTS
Rashes can be caused by either elevated
concentrations of combined chlorine
or infections from Pseudomonas
aeruginosa. In both cases, the rash is
itchy and weepy. In nearly all cases, the
cause can be distinguished based on
the time onset of symptoms. Allergic
reactions from chemical exposure begin
rapidly after exposure. In many cases,
chemical rashes can be noticed within
a few minutes after leaving the water. At
very low concentrations it may require
up to 24 hours for a chemical rash to
develop. Infections require the small
number of bacteria that enter the skin
follicle to multiply. This takes many
hours or, more commonly, several days.
If swimmers report rashes soon after
leaving the water, test for combined
chlorine concentrations. But if they
report rashes a day to a week later, there
may have been elevated concentrations
of Pseudomonas in the water. In the
first case, combined chlorine was not
being controlled. In the second case,
free chlorine was not being controlled.
In both cases, inadequate testing led to
easily preventable RWIs.
How often should you test for pH
and combined chlorine? You should
test for these every time you test for
free chlorine. The frequency of testing
will depend on the local pool code and
the venue. Some codes require testing
every two hours, while some counties in
Georgia require HOA pools to be tested
twice per week. Best practices require
operators to test frequently enough
so that the free chlorine, combined
chlorine, and pH remain within
acceptable ranges. This may require
more frequent testing than specified by
local codes. In certain areas, such as
counties in Georgia, chlorine and pH
control systems may not be capable of
maintaining proper chlorine and pH
levels without more frequent testing
and adjustment. The bottom line is
very simple: testing must be frequent
enough to comply with local codes as
well as maintain safe free and combined
chlorine and pH levels. Ultimately,
maintaining safe conditions is the
responsibility of the operator.
This article first appeared in the August 2024 issue of AQUA Magazine — the top resource for retailers, builders and service pros in the pool and spa industry. Subscriptions to the print magazine are free to all industry professionals. Click here to subscribe.
