common practice to stabilize chlorine by adding
hypochlorous acid.
ammonia to the water. The ammonia improved chlorine
retention and prolonged the life of chlorine residual test
6-3. OTHER REASONS FOR pH CONTROL.
readings, so it was reasoned that disinfection properties
were enhanced by the method. Later studies, however,
In addition to its serious effect upon disinfection and
revealed the poor disinfection properties of chloramines.
oxidation, pH fluctuation must be avoided for other
The practice has given way to a preference for burning
reasons. At high pH dissolved minerals such as iron and
out ammonia compounds through super chlorination
calcium precipitate, adding turbidity and increasing soil
(sometimes referred to as "breakpoint" chlorination).
removal demand upon the filter system. High
6-1
TM 5-662
6-6. BREAKPOINT CHLORINATION.
those of free hypochlorous acid, the loss can be at least
Breakpoint chlorination is accomplished by increasing
partially offset by maintaining higher residuals of
chlorine dosage to a point at which all ammonia
dissolved chlorine. It is generally believed that chlorine
compounds in the water are completely oxidized and
residuals in the presence of cyanuric acid should be
removed by chlorine reaction, after which point all
maintained at 1-0 to 1-5 p/lm, whereas 0-5 to 1-0 p/m is
dissolved chlorine exists as free available hypochlorous
acceptable when free unstabilized chlorination technique
acid (HOCL) or hypochlorite ion (OCL). The amount of
is practiced.
chlorine required to reach breakpoint depends upon the
b. The chlorinated cyanurates are used more
amount of ammonia present. Dosage instructions
commonly in private residential and small commercial
cannot therefore be expressed in pound or parts per
pools at this writing. In larger swimming pools that are
million. An occasional super chlorination of 4 or 5 p/m in
subject to heavy bathing loads, systems which provide
a typical pool will provide an acceptable means of
free unstabilized chlorine residual are most frequently
assuring free residual chlorine.
employed.
6-10. CONTROL OF pH AND CHLORINE
6-7. INTENTIONAL CHLORINE STABILIZATION.
RESIDUAL.
While the formation of chloramines in a swimming pool is
Oxidation and disinfection of swimming pool water can
considered objectionable, the stabilizing of chlorine with
be accomplished only when adequate chlorine residual
nitrogen compounds other than ammonia is considered
and proper pH values are maintained. The pool operator
desirable under some conditions. Such a practice may
must therefore understand what factors cause pH
seem highly inconsistent with conclusions presented in
fluctuation and chlorine dissipation and how to control
the foregoing discussion, but the benefits to be derived
those factors through proper chemical feeding practices.
become clear when the chemistry of chlorination is
carefully studied.
6-11. CHLORINATION CONTROL.
a. Chlorine consumption and feed rates are easier
6-8. STABILIZATION CHEMISTRY.
to understand than pH control. As discussed previously,
The hypochlorous acid molecule is highly desired for its
chlorine reacts with and destroys virtually all organic and
oxidizing properties, but it is a highly unstable compound
inorganic compounds in pool water. In the process, the
which rapidly dissipates in the presence of sunlight. This
chlorine itself is destroyed and must be replaced.
instability results in considerable chlorine waste, since
Therefore, the rate of feed is dependent upon the
free chlorine is rapidly destroyed even if it is not usefully
quantity of soil present in the water which, in turn, is
consumed in reactions with bacteria and soil. Some
largely dependent upon the bathing loads, bather
degree of stabilization would therefore be desirable if
preparation, weather, etc. It must also be remembered
such stabilization would slow the rate of chlorine
that free available chlorine dissipates even if it is not
dissipation without appreciably sacrificing oxidation and
consumed by soil, so some chlorine feed is necessary
disinfection activity. Recently developed practices in
even during periods when the pool is not in use.
swimming pool chlorination suggest that such
b. Generally, knowledgeable technicians and public
stabilization can be accomplished satisfactorily with the
health personnel believe that free chlorine residual of not
use of cyanuric acid as the stabilizing agent. Chlorine
less than 0-5 p/m should be maintained at all times in the
reaction with cyanuric acid produces a relatively stable
swimming pool. The better and safer practice is to feed
compound identified as chlorimide and, as in the case of
at rates calculated to provide 1 plm residual, with
chloramine formation, the dissolved chlorine exists
occasional super chlorination of 2 to 5 p m, depending
predominately as combined residual. However, the
upon ammonia content and chlorine demand of the
chlorimide possesses significantly greater oxidation and
water.
disinfection properties than the chloramine group and is
6-12. CHLORINE TEST PROCEDURE (DPD
therefore an acceptable disinfection agent, whereas
METHOD).
chloramine is not. Chlorimide reactions can also be
The presence of chlorine is tested by use of a
produced with sulfamic acid and chlorinated chyantoins,
colorimetric test using N, N-diethyl-p-phenylenediamine
but the use of these products is far less widespread than
(DPD) as a reagent chemical. The chlorine test
the chlorinated cyanurates.
procedure (DPD Method) is outlined in appendix C,
Measurement of Residual Chlorine (DPD Method). The
6-9. STABILIZATION TECHNIQUE.
test is usually made periodically with the operator
a. Laboratory and field studies of cyanuric
adjusting the chemical feed rates to compensate for the
chlorination technique suggest that, although the
rise or fall of the residual. The experienced operator
disinfection and oxidation properties of chlorimide are
learns to sense
less than
6-2
TM 5-662
chlorine demand by observing bather loads, weather
conditions, temperature, sunlight, and other influences.
upon chlorination as the principal factor. For the most
The periodic tests then are more often a confirmation of
part, it is enough to say that when pH strays from the
proper feed rates than a signal that rates need to be
ideal zone of 7-2 to 7-8, regardless of cause, it should be
changed.
promptly corrected. The operator must understand,
however, that there are conditions under which the pH
6-13.
pH CONTROL.
response to adjustment may be erratic and
unpredictable. For example, a high pH of 9-0 might be
a. The control of pH can be considerably more
adjusted to 7-8 by adding muriatic acid, only to ascend
complicated than control of chlorine concentration. The
again to 9-0 within a few hours. Or, adding a small
chemistry of the pH factor itself is considerably more
amount of corrective acid or alkali might produce a major
subtle than chlorine hydrolysis, and the factors which
response, sending the pH radically to an extreme high or
cause pH fluctuation are usually quite confusing to the
low reading. Such reactions are attributable to the "total
nonchemist. However, the methods of control can be
alkalinity" of the pool water and may indicate the need for
made reasonably clear. pH control begins with
corrections other than the addition of acid or soda ash. It
determining the pH of the water supply used initially to fill
is becoming common practice to equip swimming pools
the pool and thereafter to make up water loss. Using the
with testing equipment to measure both total alkalinity
colorimetric test with phenol red reagent, the pH of the
and pH, thus enabling the operator to make the
raw water is ascertained and then adjusted, if necessary,
necessary adjustments.
to the range of 7-2 to 7-8. Subsequent pH fluctuation is
caused largely by the type of chlorine source used for
6-15.
TOTAL ALKALINITY CONTROL.
oxidation and disinfection. Gas (elemental) chlorine, the
most commonly used chlorine source in large swimming
a. Total alkalinity might be said to be a measure of
pools, decreases pH while the commonly used calcium
the extent to which water is buffered or made to respond
hypochlorite and sodium hypochlorite sources tend to
to pH adjustment. Water containing very low total
increase pH. Thus, if gas chlorination is practiced a
alkalinity will respond radically to the addition of acid or
substance must be fed concurrently to counteract the pH
alkali for pH correction, while water containing very high
lowering effect of the gas chlorine. Soda ash, fed pound
total alkalinity might respond very little.
for pound with chlorine feed, is normally used for this
b. Generally, swimming pool water should contain a
purpose.
minimum of 80 plm and a maximum of 200 plm total
b. To counteract the pH elevating effects of sodium
alkalinity. If the test procedure indicates a need for
hypochlorite and calcium hypochlorite an acid
correction, it can usually be made by treating the water
counteractant must be used. Normally, pH control during
once, or for a short period of time, after which pH control
hypochlorination is accomplished by feeding muriatic
is routinely accomplished by the methods discussed
acid or solutions of sodium bisulphate.
above. Total alkalinity that is too low can usually be
c. The effect of chlorinated cyanurates upon pH
corrected by adding a sufficient quantity of calcium
has often been found to be very slight compared with gas
carbonate (CaC03) to bring the level to 80 plm. The
chlorine and hypochlorites. Consequently, the pH is
corrective measure for total alkalinity that is too high may
normally adjusted by occasional manual dosage of the
be somewhat more complicated. Essentially,
counteractant rather than by feeding concurrently with
undesirably high total alkalinity is corrected by adding
the chlorine source.
muriatic acid. However, a single dose of a sufficient
quantity to reduce the pH to 7-5 might not hold the pH at
6-14.
pH EFFECT.
this desired level The reading may consequently rise
again within a few hours. When such a condition
A number of other environmental conditions can affect
prevails, the acid dose must be repeated until the pH
the pH of swimming pool water, however, their
stabilizes at a desired level and total alkalinity is reduced
enumeration would probably misplace the emphasis
to less than 100 plm.
6-3
TM 5-662
CHAPTER 7
DISINFECTION AND OXIDATION PRODUCTS
7-1.
GENERAL.
Historically, chlorine has been the primary disinfectant
7-4.
CALCIUM HYPOCHLORITE.
used in swimming pools, although bromine has also
been widely used. Both chemicals are commonly
a. Calcium hypochlorite is a relatively stable
referred to as halogens, a chemical term used to
compound of chlorine and calcium, commercially
describe four related elements in the atomic table:
packaged either as a coarse powder or in tablet form. It
chlorine, bromine, iodine, and fluorine. Although iodine
is a safer material than chlorine gas with respect to
has shown promise as a pool disinfectant and is
handling and feeding, but it may present serious
currently the subject of considerable experimentation, its
problems if spilled or scattered in a moist or wet
use has not become widespread enough to be included
environment or if oxidizable material is introduced to the
in this discussion. Algicides are used to assist the
container. When applied to swimming pool water
disinfection process and are therefore included. All pool
calcium hypochlorite reacts much the same as chlorine
chemicals must be handled and stored in accordance
gas. It tends to release free chlorine from the stabilizing
with the manufacturer’s instructions. NOTE: Never mix
agent and the resulting hydrolysis produces varying
chemicals together outside of the pool; rather use the
chlorine reactions. Due to the relatively compact nature
pool as a buffer in the actual application.
of the package material, calcium hypochlorite is a
popular chlorine source in small-/medium-sized
7-2.
CHLORINE PRODUCTS.
swimming pools. Although it is a more costly source
than gaseous chlorine (in net yield), this disadvantage is
Chlorination, as the term implies, is the practice of
somewhat offset by the relative ease and safety of
introducing chlorine to pool water after it leaves the
handling, storage and feeding. The most commonly
equipment either in its elemental form or as a chlorine-
used calcium hypochlorites will yield 70 percent available
bearing compound. Regardless of the product used or
chlorine by weight.
the method of application, the goal is to achieve a
b. Calcium hypochlorite can be manually fed
chlorine residual possessing strong oxidizing and
directly into the pool from hand-held containers to either
disinfecting properties. There are four chlorine sources
facilitate super chlorination or as an alternate feed in the
that are commonly accepted as disinfection products.
event of equipment failure. Normally, however, it is
mixed with water in tanks or feed crocks and the clear
7-3.
ELEMENTAL CHLORINE.
liquid is fed to the recirculation system by mechanical
a. Elemental chlorine is a greenish gas at room
feeders. Such feeders are adjustable to control rates of
temperature. Packaged under pressure as a liquid in
continuous or intermittent feed.
metal bottles, it is fed into the recirculation system by
specially designed equipment. If the chlorine gas
7-5.
SODIUM HYPOCHLORITE.
escapes from the container or feeder apparatus, it will
aggressively attack virtually all surroundings, especially if
a. Sodium hypochlorite is a liquid compound of
water or moisture is present. It is also highly toxic to
chlorine, water and sodium which is usually packaged in
man. Because of the hazardous nature of chlorine gas,
carboys or drums. If properly stored, it will yield 10
its proper handling must be thoroughly understood by
percent to 15 percent net chlorine depending upon its
those responsible for handling containers and operating
method of manufacturer and the age of the material.
feeding devices.
Like calcium hypochlorite it is relatively safe and easy to
b. Normally, the cost of elemental chlorine is
handle and feed, but it is also a hazardous product to
considerably less than the cost of commercial chlorine
spill. Applied to pool water the hydrolysis reactions are
bearing compounds. It is therefore the most commonly
essentially like those of other chlorine sources.
used chlorine sources in the large swimming pools
b. Because of the weight and bulk involved, sodium
where feed rates and consumption are high. The cost of
hypochlorite normally is used to chlorinate smaller pools
the extra soda ash required for this type of chlorine must
ranging in size up to 75,000 gallons. For disinfection
be taken in account in making any cost comparison.
purposes its use with respect to pool size is limited.
c. Mechanical feeding is accomplished in the same
manner and by the same type of equipment used to feed
the mixture of calcium hypochlorite and water.
7-1
TM 5-662
Sodium hypochIorite need not be premixed with water. It
c. Commercially, elemental bromine is packaged in
is a feedable liquid in its packaged form when the proper
glass jugs specially crated to guard against shock
feeder is used.
damage and breakage in shipment and handling. The
material is fed to the recirculation system through a
7-6.
LITHIUM HYPOCHLORITE.
brominator which dissolves the liquid bromine in a crock
Lithium hypochlorite is another of the dry chlorine
of water near the point of injection. Elemental bromine is
compounds. It is a free-flowing granular sanitizer
more costly for equivalent disinfection values than gas
containing 35 percent available chlorine. The product is
chlorine, and normally more expensive than the
an inorganic material with the chlorine immediately
hypochlorites and cyanurates.
available as in the other inorganic chlorine vehicles. It is
completely soluble in pool water or may be made up in a
7-9.
ORGANIC BROMINE.
solution and dispensed through a chlorinator.
a. In recent years bromine has become available
Stable under all normal storage conditions, it may be
commercially for pool sanitation in bromine-coating
stored for extended periods without appreciable loss of
organic compounds commonly referred to as hydantoin
available chlorine. It is an acceptable product for
or "stock" bromine. In such forms bromine can be
swimming pool sanitation and has all the attributes
compared with hypochlorites and cyanurates except it is
common to the other hypochlorites.
twice as heavy as chlorine but not as volatile in the pool
atmosphere. Such-products are more costly than
7-7.
CHLORINATED CYANURATES.
elemental bromine and therefore less likely to be used in
a. Chlorinated cyanurate is a relatively new pool
large swimming pools. They are far less hazardous to
disinfection product and is not widely used in swimming
handle than elemental bromine, however, and therefore
pools.
possess distinct advantages in dosing smalland medium-
b. Chlorinated cyanurate is available commercially
sized pools where cost is a lesser consideration.
in both white powder and tablet form. The most
b. Organic bromine is more costly than most of the
commonly marketed cyanurates contain from 60 percent
disinfection products discussed here. It is a slowly
to 85 percent available chlorine. The physical
dissolving solid which is normally fed to the recirculation
appearance, handling precautions, and techniques of
system from a pressure vessel by the washing action of
feeding, etc., of this group of chlorine-bearing
the recirculating stream of water. As a practical matter,
compounds are the same as calcium and sodium
the organic bromine compounds may be less adaptable
hypochlorite. The important product differences involve
to precisely controlled feed rates unless metered by
the chemistry of hydrolysis. The cyanurates provide
positive displacement devices. The method has been
chlorine residual which is relatively more stable and
systematically effective, however, in disinfection of
therefore longer lasting in pool water than that provided
private pools. Also, claims have been made that longer
by elemental and hypochlorite forms. Although such
swimmer immersion can be effected, which is a factor for
stability reduces disinfection and oxidation properties, it
competitive and training pools.
may be desired for other reasons. Cyanurates are an
advantage when chlorination is accomplished by
7-10.
ALGICIDES.
intermittent hand feeding rather than by continuous
If the pool water takes on a greenish or mustard-colored
mechanical application.
cast or black or dark green spots appear on the surface
finish, algae is probably present and an algicide should
7-8.
ELEMENTAL BROMINE.
be used. An algicide is a chemical additive used to kill
a. Pure elemental bromine is a heavy, red liquid
and prevent the growth of algae in swimming pool water.
and, like chlorine, is an aggressive oxidizing agent.
Algicides are formulated for their specific toxicity to algae
Bromine is a dangerous chemical in untrained hands. If
as an aid to disinfection chemicals. Although algae
spilled from its container, bromine will attack virtually all
growth can be inhibited by disinfection chemicals alone,
surroundings. Even the fumes from an uncapped
there seems to be increasing acceptance and use of the
container can injure people and damage surroundings.
algicides for reasons of economy because their use
Any person exposed to bromine fumes should be
reduces chlorine demand. Since mercurials have been
checked by the base health department.
banned by The Environmental Protection Agency (EPA),
b. As a disinfection product, bromine has been
phenol mercuric acetate cannot be used. Quaternary
demonstrated to be equal to chlorine in bactericidal
ammonium halides are not recommended as they may
efficiency, although the chemistry is somewhat different.
cause foaming, absorb on filter media, and increase
The hydrolysis of bromine produces hypobromous acid
chlorine demand. Copper compounds are ineffective
which, like the hypochlorous acid product of chlorination,
against some algae. Copper sulfate can cause skin
is the agent which destroys bacteria and oxidizes
rash and turn hair green at high
undesirable soil.
7-2
TM 5-662
concentrations as well as cause milky or inky precipitates
limitations which need not be discussed here. The
in highly alkaline or sulphur-containing waters. Other
primary shortcoming is the relatively prolonged "contact
copper salts can be considered safe to use if
time" required for bacterial kill. It is also noted that silver
manufacturer’s instructions are strictly followed.
has very limited oxidizing properties which, as discussed
previously, are essential to overall treatment of pool
7-11.
PRODUCTS.