Pool Disinfectants and pH

7/31/2019 Pool Disinfectants and pH

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18Pool Disinfectants and pH

Pool Dis infect ant s and pH

CHAPTE

R

3LEARNING OBJECTIVES

Because of waterborne outbreaks of typhoid, cholera,

and hepatitis, health scientists have emph asized the n eedto treat water that is used for human consumption orrecreation. Chlorine and a few other chemicals, whenused prop erly, act as disinfectants and p revent the spreadof several comm un icable diseases.

The most comm on m ethod of disinfection is with chlo-rine-based (chlorinated) products. There are several dis-infectants approved by public health officials for use inpu blic swimming p ools to control disease and to maintainspecific sanitation stand ards. These d isinfectants are con-sidered pesticides and must be registered for use by theEPA and used according to their label. In ad dition, to be

After completely studying this chapter, you should beable to:

s Define oxidation and sanitization.

s Name 3 forms of chlorine-based disinfectants usedfor sanitizing p ool water.

s List the minimum safety requirements for chlorinegas use.

s Explain wh at a stabilizer does for chlorine.

s List 4 types of sanitizers or oxidizers ap proved foruse in public pools.

sList the disadvantages of using ozone, ultravioletlight, or silver-copp er ionization as a disinfectant.

s Know the imp act of low or high p H levels on poolwater.

s Und erstand how the add ition of various chemicalschanges the pH of the pool water

s Explain two method s for controlling pH .

used in Michigan pesticides must be registered by theState of Michigan through the Departm ent of Agriculture.

Other types of chemical disinfectants are available, aswell as non-chemical methods of disease control. Usedalone, some of these methods are not app roved by pu blichealth officials for public pool maintenance. Ozone,iodine, ultraviolet light, and silver are among this groupof unapproved sanitizing products. However, thesemethods could be u sed in conjunction w ith a chlorinatedproduct, or equivalent, to provide acceptable and ade-quate pool sanitation.

When h and ling chemicals, always w ear personal pro-tective equipment (PPE). Many of the chlorine-basedchemicals have extreme pH propertiesvery acidic orvery alkalineand can cause severe injury to the han dlerif contact is made with unprotected skin. When using

pool chemicals, remember the following:1. When han dling chemicals wear p rotective gloves,

eyewear and clothing.

2. Read the chemical label before opening the p ack-age. Understand the directions for use and safetyinformation before starting an application.

Store chemicals in their original containers in a cool, dryand secured location.


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19 Pool Disinfectants and pH

3 Chemicals used for d isinfection mu st be continu ous-ly fed into public pools by an automatic feedingsystem.

4. Chemicals are mixed into the target body of water.Never ad d w ater to a chemical.

5. Never mix chemicals with other chemicals unlessspecified and permitted by the labels of each.

6. Store chemicals in their original containers in a cool,dry and secured location.

Chlor ine-based Pool Disinfect antsWhen chemicals containing chlorine are added to

wa ter, an active chemical is formed called hypochlorousacid (HOCl). The H OCl molecule is an extremely power -ful oxidizing (capable of destroying or burning up theorganic debris) agent. It destroys har mful organ isms suchas bacteria, algae, fungi, and viruses, along with impuri-ties too small to be removed by filtration.

s The action of HOCl that destroys harmful organ-isms is called sanitization .

sThe action of HOCl that d estroys the impu rities notremoved by filtration is called oxidation .

Using a chlorine-based chemical is considered a typeof pesticide application or pesticide treatment. Beforeusing any chemical, read the label on the container, thematerial safety data sheet, and all pertinent information.

Any chlorine-based product used in a public swim-ming p ool must be labeled for that purp ose and approvedby the MDEQ. Chemicals used for disinfection must becontinuously fed into the pool by an automatic feedingsystem. Adding chlorine-based chemicals to a pool byhand (hand feeding) is NOT allowed.

Chlorine-based chemicals must be fed continuously into thepool by an automatic or semi-automatic feeding system.

Chlor ine Gas [Cl2]The laws and liability surrounding the use of chlorine

gas make it one of the most expensive disinfectants touse. Because of the extreme risks involved with chlorinegas, its use is notjustified for sw imming pool operat ion swhen alternative disinfectants are available. Using chlo-rine gas for pool disinfection is an out-dated m ethod an dno longer recomm ended .

Chlorine ga s is extremely toxic. Chlorine in gas form is100% available chlorine by w eight. The gas is pale greenin color, heavier than air and is deadly if improperlyused, handled, or stored. Chlorine gas is packaged andcontained in pressurized steel cylinders. Chlorine in gasform, has a pH of 0 to 2extremely acidic. Therefore, atremendous am ount ofsoda ash (pH increaser) is neededto control the pH of the water w hen it is chlorinated withchlorine gas.

No new or refurbished gas chlorine systems can beinstalled without MDEQ approval. There are fewer thansix such systems in use within Michigan, and they arebeing replaced with safer, more economical methods ofdisinfection. Although , existing chlorine gas system s are

allowed to continue operation, operators are encouragedto replace them with safer chlorinating systems.

The following is an overv iew of some of the minimu msafety requirements for chlorine gas use:

1. Chlorine gas cylinders mu st be chained or securedto a rigid su pp ort to prevent tipp ing.

2. Chlorine gas should always be stored w ithin a fireresistant room or building.

3. The storage room mu st be designed to keep thetanks and chlorinator separated from any otherequipment or chemicals.

4. The storage room or building mu st have proper

ventilation capable of a complete air change withinone (1) to four (4) minutes.

5. An app roved self-contained air supp ly (gas mask)mu st be kept just outside the storage room at alltimes.

6. Check the chlorine gas cylinder and the chlorinatorfor leaks da ily. While wearing personal protectiveequipment (PPE), including a self contained airsupp ly mask, use a small amount of householdammon ia on a cloth and rub over the equipmenthose connections and regulator. In the p resence of achlorine leak, this produ ces a white vapor.

7. Use a new lead gasket each time a new cylinder is

pu t into service to prevent possible gas leaks.

The suns ultraviolet rays quickly degrade chlorinegas. In bright sunlight in a two hour period, 97% of thechlorine can be degraded from the swimming pool. Awater stabilizer, such as cyanuric acid, can be used tomake the chlorine last longer.


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Calcium Hypochlor it e [Ca(OCl) 2]Calcium hypochlorite [Ca(OCl)2] is 65% by weight

available chlorine. It is available in granular, stick, andtablet formulations. Calcium hypochlorite has a pH of11.8very basic. Therefore, when using calciumhyp ochlorite as your d isinfectant, the pool water requiresmuriatic acid or sodium bisulfate to lower the pH of thepool w ater to th e desirable ran ge of 7.2-7.6.

If used for a shock treatmen t (raising th e d isinfectantabove normal maintenance levels), calcium hypochloritemust first be dissolved in water, then applied into thepool as a liquid. If directly applied to the pool as a gran-ular p roduct, cloud iness of the w ater may result. Applystick and tablet formulations only through an au tomaticdispenser. The suns ultraviolet rays also degrades thisprodu ct in a short p eriod of time.

Calcium h ypochlorite mu st be kept in a d ry cool area,free of contamination. If this chemical comes in contactwith an organic compound, fire could result. If a fireoccurs, the smoke (gas) is very dangerous.

Sodium Hypochlor it e [NaOCl]Sodium hypochlorite [NaOCl] is a liquid chlorine. It

is a clear, slightly yellow material providing 10% to 15%available chlorine (1 lb. of chlorine per gallon). This liq-uid chemical has a pH of 13 and causes a slight increasein the pH of the pool water. To maintain prop er pH lev-els in the pool water when using sodium hypochlorite,add mu riatic acid or sod ium bisulfate.

Sodium hypochlorite is considered the best choice forshocking (quickly raising the disinfectant above normalmaintenance levels) swimming pools, sanitizing decks,and shower/ locker rooms. It is more economical and saferthan other chlorine-based disinfectants. Sodium hypochlo-

rite is not stable in storage and gradually loses strength. Ifstored in a dark cool room, it has a one-month shelf-life.

The suns rays also degrade sodium hypochlorite.Unless a chlorine stabilizer is used in conjunction withthe sodium hypochlorite, it is not considered economicalfor use in ou tdoor swimm ing pools.

When sodium hypochlorite is part of your p ool main-tenance program, it is recomm ended to:

s Store only a 30 day supply of sodium hypochlorite.

s Keep the chemical in a cool dry area, out of directsunlight.

s Always personal protective equipment when han-

dling the chemical.s Immediately wash off any chemical splashed on the

clothing or skin.

Chlor inated Isocyanur ate(st abilized chlor ine)

Chlorinated isocyanurate is available in three formsgranular, tablet, and stick. The granular form is calleddichloro-isocyanuric acid and contains 55% or 62%available chlorine. The stick and tablet forms generally

contain 89% available chlorine and are called trichloro-isocyanuric acid.

Dichloro-isocyanuric and trichloro-isocyanuric are both

stabilized chlorines. The isocyanurate portion of theproduct is the stabilizer, sometimes called the cond itioner.The stabilizer protects the chlorine from ultraviolet (UV)rays of the sun, allowing the chlorine to last longer.

The dichloro-isocyanuric acid granular material with55% active chemical remains fairly stable once in th e poo lwater. The 62% dichloro-isocyanuric acid formulationmust be labeled as an oxidizer and is not as stable as the55% material. Dichloro-isocyanuric acid has a pH of 6.9and should n ot affect the pH of the pool as much as otherproducts. It is very slow to dissolve, especially in waterbelow 76oF. This is because the cyanur ic acid comp onentacts as a blanket, surrounding each chlorine molecule,

protecting it from the sun and allowing the chlorine todissolve slowly. Thu s, chlorine is more consistently avail-able in the water.

Trichloro-isocyanuric acid sticks and tablets can only befed into the pool water by a pressure feeder approved bythe MDEQ and National Sanitation Foundation (N.S.F.).These sanitizers cannot be placed in the skimmers or hairand lint strainer as a means of feeding (application).

Cyanuric acid has no chlorine content. Yet, by main-taining a cyanu ric acid concentration level of 30-40 ppmin pool water, any chlorine product will last up to fourtimes longer. This concentration is measu rable by u sing atest kit. The public health department has set the recom-mended level of cyanuric acid at 30-80 ppm. Routinelytest cyanuric acid levels to insure the concentrationremains w ithin recommend ed guidelines. Cyanu ric acidlevels can be increased in a pool, but cannot be d ecreasedwithout either adding specific chemicals or draining thepool and add ing new w ater.

Cyanuric acid products are not recommended forindoor pools and spas, since the need for chlorine protec-tion from the sun is not a concern.

NEVER condition or stabilize pool water with cya-nuric acid when using bromine as a sanitizer. Cyanuricacid and bromine are not compatible chemicals.

Chlorine is available in granular, tablet, stick, and liquid form.


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Lit hium Hypochlor it e (LiOCl)Lithium hypochlorite (LiOCl) is a fairly new p rodu ct in

the field of pool water disinfectants. It contains only 35%available chlorine, is more expensive than most chlorinatedproducts, and has a pH of 10.7. The addition of lithiumhypochlorite to pool water increases the pH of the water.Lithium hyp ochlorite has excellent stability and w orks wellin hard pool water w ithout causing cloudiness.

Operators mu st take the same safety precautions w henusing lithium hypochlorite as when using calciumhypochlorite. Lithium hypochlorite can be stabilized byusing it in combination with cyanuric acid, but thismakes the end produ ct more expensive.

Br omine-Based Pool Disinfect ants

Br omine and Hypobr omous Acid (HOBr )Bromine is a liquid in its pure, elemental form. Only

bromine compounds are available for pool water disin-fection since the pure form is too hazardous to handle.

When bromine comp ound s are add ed to water, the add i-tion or presence of an oxidizer is required to form hypo-bromous acid (HOBr) and hypobromite ions (OBr-).Hypobromous acid (HOBr) is the active oxidizing(killing) form of bromine that controls bacteria, algae,and other m icroorganisms. Hypobromite ions (OBr-) area relatively inactive form of brom ine.

For pool sanitation, bromine compounds are sold intwo solid formulations. There is a two-part bromine sys-tem consisting of a bromide salt, which when dissolvedin water, requires the addition of a separate oxidizer thatactivates it. There also is a one-part stick or tabletbromine formu lation that contains both bromine and anoxidizer and is dispensed by an erosion-type feeder.

Bromine is commonly used in tablet form. Bromine for-mu lations usually contain 62% bromine and 27% chlorine(remember, chlorine is an oxidizer).

Bromine formulations have a pH of 4.0 4.5, whichlowers the pool w aters pH . Therefore, soda ash mu st beused in conjun ction with bromine to adjust the pH of thepool water.

Bromine is not as effective in oxidizing organic matteras chlorinated produ cts especially ou tdoors w here ultra-violet (UV) rays quickly destroy bromine residuals. Toda te, there is no UV stabilizer for bromine.

All of the chemicals discussed so far are approved byMDEQ for use as disinfectants of public bathing waters.Contact your local MDEQ about other chemicals used assanitizing agents to d etermine approp riate uses.

Other Types of Sanitizer s or Oxidizer sIn addition to chlorinated chemicals and bromine,

there are other disinfectants and disinfectant devicesused in pool maintenance operations.

IodinePotassium iodine is a white, crystal chemical. This

chemical needs an oxidizer, such as h ypochlorite, to reactwith organic debris and bacteria. Iodine does not reactwith ammonia, bleach hair or bathing suits, or cause eyeirritation, but it can react with metals producing green-

ish-colored p ool wa ter.

OzoneOzone (O3) is a gas. Ozone is an effective germicide

with 50% greater oxidizing activity than chlorine. Ozoneproduces no residuals since unconsumed ozone gasreverts to oxygen (O 2). Ozone does not effect the pH ofthe pool water.

Ozone systems work in conjunction with the filtrationsystem. Ozone is fed into the pool by a mechanicaldevice. All ozone units, at the time of this printing, mustbe used in combination with a conventional disinfectingsystem to meet MDEQ requirements.

Ozone has a mild odor. It can cause eye, nose, skin,and respiratory problems at a concentration of .05 .1pp m, especially in a poorly vent ilated area. There are twomethods of producing ozoneUV (ultraviolet), andCorona Discharge. Its use is tightly regulated to assurebather and operator safety. MDEQ approval is requiredprior to ozone equipm ent installation.

Summary Disinfectant Table

*Gase Sodium Calcium Lithium Dichlor Trichlor BromineChlorine Hypochlori te Hypochlori te Hypochlori te

% Available 100% 12-15% 65-70% 35% 56% or 62% 90% 94% HOBr inChlorine water pH 7.5

pH effect Lowers Raises Raises Raises Neutral Lowers Lowers(pH >1.0) (pH 13.0) (pH 11.8) (pH 10.7) (pH 6.9) (pH 2.9) (pH 4.0-4.5)

Lost tosunlight Yes Yes Yes Yes No No Yes

Physical Gas Liquid Granular Powder Granular Granular 2-part solidAppearance & Tablet & Tablet or Tablet


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Ult r avioletUltraviolet (UV) radiation is a means of killing bacte-

ria. Pool water passes by the ultraviolet light that acts asa bactericide. It is not a new concept in sanitizing.Ultraviolet and ozone systems have been u sed in Europefor many years.

The success of the UV system is based on water clari-ty. If the water is cloudy, the rays of the ultraviolet arescreened and therefore not as effective. The greatest p rob-lem that health departments have with ozone and ultra-violet systems is a bactericidal (disinfectant) residu al can-not be m aintained and that these systems h ave little or noeffect on algae. Therefore, UV systems are approved foruse only in conjunction with conventional disinfectionsystems.

Elect r olyt ic CellsElectrical deviceschlorine generatorswere devel-

oped to manufacture chlorine. Chlorine is manufacturedby electrolysis of sodium chloride (NaCl, salt) that is d is-solved in water. This process also produces sodium

hydroxide (NaOH). When chlorine gas (Cl2) and sodiumhydroxide come in contact with each other, they formsodium hypochlorite (NaOCl), or what is commonlycalled liquid chlorine. Units currently available on themarket generally have very limited chlorine output.Because of this, multiple units may be required to pro-du ce desired residu als.

Silver -Copper Ionizat ionSanitizing can be accomplished by using an ionizing

unit that introduces silver and copper ions into the waterby electrolysis, or by passing an electrical curren t throu gha silver and copper electrode. The limiting factors in u sing

this system in the pool and spa industry are cost, a slowbactericidal action and potentially high contaminant lev-els caused by bather loads. Also, wh en using this system,if the prop er param eters of water chem istry are not m ain-tained, black spots form on pool surfaces. To insure thatall debris in the pool has been oxidized and the harmfulbacteria destroyed, an approved chemical disinfectantmust be used in conjunction with an ionizing unit.

FlocculentsAluminum sulfate (Al2(SO4)3), is commonly used as a

filter aid and coagulant (gathers and precipitates sus-pended matter), as well as a settling agent for cloudy

water. Aluminum floc is a white gelatin-type substancethat attaches itself to free floating matter found in water.This creates a larger, heavier particle that settles to thebottom (precipitates) of the pool or may be captured onthe surface of the filter. The layer of accumulated debriscan then be vacuumed.

There are several typ es and styles of flocs and clarifierson the market, and all aim for the same goal. Alwayscheck the filter pressure before adding a flocking agen t toany type of filter. The pressu re inside the filter will buildrapidly after the flocculent is added. When the pressureinside the filter becomes 10 12 lbs. (psi) greater than

normal, shut d own the system an d backwash the filterto waste. Backwashing (process of cleaning a pool filterby reversing the flow of water throu gh it), or add ing theflocculent may need to be repeated several times beforeacceptable w ater clarity is achieved.

Sequester ing AgentsPools with high iron content require a sequestering

agent as part of their routine water treatment. By coat-ing or chemically reacting with the ion, a sequesteringagent increases the ability of the water to h old the m iner-al in solution instead of precipitating out of the solution.When minerals precipitate out of the water, stains formon walls and floors of the pool.

pHWhen a water molecule (H 2O) breaks down, a p ortion

of it breaks into electrically charged par ticles of hyd rogen(H+) called hydrogen ions. The remainder is brokendow n into hyd roxyl ions (OH -). The pH reading is a mea-

sure of the hydrogen ion (H+) concentration in the poolwater. The pH scale ranges from 1-14, with 7 being neu-tral. Anything with a numerical value less than 7 is saidto be acidic and a numerical value greater than 7 is con-sidered alkaline. pH read ings also can be described as theacidity-alkalinity relationship. A change in pH of 1.0(such as from 7.0 to 8.0) represents a tenfold chan ge in theion concentrations. For example, the hydrogen ion con-centration of water with a pH of 7.0 is ten times that ofwa ter w ith a p H of 8.0, and is 10 x 10, or 100 times greaterthan that of water w ith a pH of 9.0.

When certain chemicals are dissolved in water theyreact to form either more hyd rogen ions or hyd roxyl ions.Chemicals that produce hydrogen ions (H+) are calledacids. Chemicals that produce high concentrations ofH+ ions are considered strong acids, w hile those prod uc-ing lower concentrations of H+ ions are weak acids.

Chemicals that produce hydroxyl ions (OH-) in thewa ter are labeled as alkalines or bases. Again, chem -icals that produce high concentrations of hydroxyl ionsare strong bases while those that produce lower concen-trations are weaker bases.

The pH of water is affected by the acidic or alkalinechemicals dissolved in it. Hypochlorite solutions, sodaash, and sodium bicarbonate raise the pH . Chlorine gas,alum, muriatic acid, cyanuric acid and sodium bisulfatelower the pH .

Chemicals that Chemicals thatCause an Increase in pH Cause a Decrease in pH

s Hypochlorite solutions s Alum

s Soda ash s Muriatic acid

s Sodium bicarbonate s Cyanu ric acid

s Sodium bisulfate

s Chlorine gas


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THE EFFECT OF pH ON POOL WATER

Using Mur iatic AcidDecreases pH

Using Soda Ash orSod ium Bisulfate

Increases pH

Increasinglyacidic

Neutral Increasinglybasic

1

6.8 7.0 7.2 7.4 7.6 7.8 8.0 8.2 8.4

2 3 4 5 6 7 8 9 10 11 12 13 14

POOL WATER ZONE

s pH too low

s corrosivechlorinelost

s irritating

s pH idealneutral

s maximumumchlorineefficiency

s comfortzone

s pH to high

s scale forming

s chlorine lesseffective

s irritating

Significance of pHThe pH of the water greatly influences certain chemi-

cal reactions, such as those involving chlorine andbromine. Since HOCl and HOBr are acids, they can beneutralized with alkaline materials and their effective-ness decreased. These acids are said to be pH sensitive.As the pH of the water increases (becomes more alka-line), the effectiveness of chlorine and bromine decreases.

For example, the disinfecting action of chlorine in waterwith a pH of 8.0 is only one-fourth as fast and effective aschlorine in water with a pH of 7.0.

The effectiveness of chlorine and bromine dependsupon the respective proportions of available hypochlor-ous and hypobromous acids, which, in turn, dependsupon the pH of the treated water. Table 3.1 outlines thepercent of active and inactive forms of HOCl and OCl-,and HOBr and OBr- based on th e pH of the treated w ater.

Accurate control of the w aters pH is essential for sanitiz-ers to be effective. According to the Michigan PublicSwimming Pools Act 368, swimming pool water must bemaintained between 7.2 to 8.0. How ever, a pH range of 7.2to 7.6 is more p ractical from a m anagem ent stand point.

Chlorine and bromine both are more effective sanitiz-ers when the pH is between 7.2-7.6.

The waters pH also influences the likeliness of scaleor w ater hardn ess depositsdeposits increase as the pHincreases. Hardness (water) refers to the quantity of dis-solved minerals, chiefly calcium and magnesium thatmay be deposited as scale. Deposits can be very trouble-some in the pool filter, heater, piping and even the poolitself. See chapter 6 for more information on water hard-ness.

Swimm er irritation increases as the pH gets above 8.0.

If the pH becomes too low, the water becomes aggres-sive and even corrosive. Irritation to swimmers eyes,mucous membranes, and skin may result regardless if lit-tle or no chlorine or bromine residuals are in the water.Low water pH is the most common cause of swimmerirritation problems.

Maintaining the ap propriate pH level is a key part ofkeeping the pool w ater balanced an d stable.

pH HOCI OCI- HOBr OBr-

H+ Hypochlorous acid Hypochlorite Ion Hypobromous acid Hypobromite Ion

Hydrogen Ion (killing agent) Inactive (killing agent) Less active

Active Active

pH % Ch lorie as H OCI % Ch lorin e as OCI- % Brom in e as H OBr % Brom in e as OBr-

6.5 90 10 99.4 0.6

7.0 73 27 98 2

7.5 56 44 94 6

8.0 21 79 83 17

8.5 10 90 57 43

Table 3.1 Effect of pH on Hypochlorous and Hypobromous acid concentrations.


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Recommended pH levels:Maintain the pH of the pool water between 7.2 to 7.6.

It is preferable not to exceed 7.6 since the pH of swim-mers eyes is 7.5. Also, as stated above, the effectivenessof the disinfectant in the pool changes with pH levels.The following chart states the disinfectant residual thatmu st be maintained at various p H levels to maintain ade-quate cleanliness of the water.

Type of pH pH

Disinfectant Residual 7.2-7.6 7.6-7.8

Bromine Bromine 1.0 ppm 2.0 ppm

Chlorine Free Chlorine 0.4 ppm 1.0 ppm

Chlorinated Free chlorine 1.0 ppm 1.5 ppmcyanurate

Maintaining pH LevelsWhen a swimming pool is filled, test the pH of the

water. Usually, the incoming water is suitable for swim-ming pool use with little or no adjustment. Expectchanges in the pH with daily use of the pool. The addi-tion of make-up water, swimm ers wastes, and acidicpool chem icals all effect the p H of the w ater.

The addition of pool chemicals is necessary to bal-ance the water and get the pH back to the desired level.Daily addition of enough fresh water to raise the poolwater level three or four inches, is an effective, conve-nient, inexpensive way of maintaining the optimum pHrange for many swimm ing pools.

If adding m ake-up wa ter is ineffective at regaining thedesired pH, a chemical must be added to the water for

pH m anagement.

There are two methods for controlling pH in poolwater.

1. Manually the pool operator applies the proper pHadjusting chemical (this d oes not includ e chlorine)into the pool wh ile wearing all the app ropriate PPE.

2. Automatically using an au tomatic pH controllingdevice operated in conjunction with other poolequipment.

In smaller pools (less than 50,000 gallons), to decreasepH it is recommend ed th at sodium bisulfate is used sinceit is less toxic than other products. Use muriatic acid todecrease pH in larger p ools where automatic systems areavailable to feed it into the p ool water. Muriatic acid is acaustic chemical, wear extra personnel protective equip-

ment including goggles when handling it. It is veryimportant not to splash muriatic acid onto your skin orclothing, or into your eyes.

The amoun t of chemical needed to lower pH is deter-mined with an acid demand test kit. To properly testthe waterier, a measu red am oun t of pool water is coloredwith phenol red from the pH test kit. Then a reagent(acid) is added u ntil the color changes to match the colorof the desired p H level as shown by th e kit. The amountof reagent used in this test is compared with a chart.Knowing the pool volume and using chart information,the amou nt of chemical needed for lowering pH is deter-mined.

Sodium bisulfate (NaHSO4

) can be used for pH andalkalinity reduction in sm all pools. It is a wh ite, odo rless,crystalline material known as a pH reducer. Liquidsolutions of sodium bisulfate are highly acidic. Handlewith care and wear appropriate personal protectiveequip men t. Use it only after the pool is closed for the d ay,since it destroys chlorine residuals which will need to beadjusted before bathers return.

Use an acid d emand test kit to determine the amoun tof sodium bisulfate or muriatic acid to apply to the poolwater to lower the pH. If the chart with your kit showsonly the amounts of muriatic acid to use, 1 1/4 lbs. (20ounces) of sodium bisulfate can be used for each pint ofmuriatic acid recommended. For example, if 2 pints of

muriatic acid are recommended, apply 2 1/2 pounds ofsodium bisulfate to create the equivalent pH chan ge. If anacid demand test kit is not available, use about onepound of sodium bisulfate per 10,000 gallons of water tolower pH .

Amount of Sodium Bisulfate oz ./1,000 gal. pool volume

Current to lower to a desired pH of:

pH level 7.0 7.5 8.0

8.0 1.4 0.4

8.5 1.6 0.8 0.3

9.0 2.3 1.3 0.9

9.5 4.0 3.1 2.6

10.0 6.9 5.9 5.5

GUIDE TO LOWERING pH WITH SODIUM BISULFATE:


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Guide to Raising pH:

One p ound (16 ounces) ofsodium carbonate (sodaash) per 10,000 gallons will raise the pH 0.3.

One p ound (16 ounces) ofsodium bicarbonate(baking soda) per 10,000 gallons will raise thepH 0.10.

Example: To determine the amount ofsodium carbonate(soda ash) needed to increase pH from 7.0 to

7.5 in a 24,000 gallon swimming pool.

24,000 gallons= 2.4; 7.5 7.0 = 0.5;

.5= 1.67

10,000 gallons .3

1.67 2.4 16 ounces = 64.13 ounces or4 lbs. soda ash

Example: To determine the amount ofsodiumbicarbonate needed to increase the pH from7.0 to 7.5 in a 24,000 gal. swimm ing p ool:

24,000 gallons= 2.4; 7.5 7.0 = .5;

.5= 5

10,000 gallons .3

5

2.4

16 ounces = 192 ounces sodiumbicarbonate

192 ounces = 12 pou nd s of sodium b icarbonate

A single app lication of sodium bicarbonate should n otexceed (2) two p oun ds p er 10,000 gallons. Test the p H 30to 60 minu tes after app lication.


Example: To determine the ounces ofsodium bisulfateneeded to lowerthe pH of a 24,000 gallonswimming pool from pH 9.0 to 7.5:

1.3 ounces 24 = 31.2 ounces

Note:Add ing 20 ounces of sodium bisulfate has th eequivalent effect as ad ding 16 ounces (1 pint) ofmuriatic acid.

While wearing PPE, apply sodium bisulfate (to lowerpH) with a scoop by scattering or broadcasting the pre-determined am ount directly onto the pool water surfacein the deeper area. The pH may d rop quickly du e to theformation of carbon dioxide but then rise again as thecarbon d ioxide escapes into the air. For this reason, recir-culate the water while testing to determine the effective-ness of the treatment and if there is a need to repeat thechemical addition.

Liquid acids, including muriatic acid (commercialhydrochloric acid), are not recommended (unless used inautomatic feed systems) for pH adjustment because ofthe safety hazards inherent with han dling. If you d o use

muriatic acid, impermeable gloves and safety glassesmust be worn to keep the acid away from the skin andeyes. Eye injuries and acid bur ns hav e resulted from fail-ure to observe these p recautions. Liquid acid ap plicationsshould not exceed one quart per 10,000 gallons of waterin any one treatment. If automatic feed systems are notavailable, dispense the liquid close to the water s surfaceto prevent splashing and apply it to the deepest area ofthe pool. Keep swimmers out of the water for severalhours after each application.


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Write the answers to the follow ing questions, then

check your answers w ith those in the b ack of the

manual.

1. Match the terms sanitization, oxida tion, stabilizer,flocculent, and sequestering agent w ith the ap propri-ate definition.

___ San itization A. A ch em ical th at, w henadd ed to pool water,keeps d issolved m etalsand minerals in clearsolution (suspend ed).

___ Oxid ation B. Cyanuric acid , alsoknown as conditioner, thatslows sunlight from dissipating chlorine strength.

___ Stabilizer C. A comp ound usu ally usedwith sand-type filters toform a thin layer ofgelatinous substance on thetop of the sand , helps trap

fine su spend ed particlesthat might pass through thesand.

___ Floccu len t D. Th e ch em ical p rocess th atdestroys organic contaminants in pool water notremoved by filtration.

___ Sequestering E. The action of the chemicalagent hypochlorous acid (HOCl)

that destroys harmfulorganisms in the p ool water.

2. List 5 minimum safety requirements for chlorine gasuse.

Review Questions

Pool Disinfectantsand pH

3. Why is stabilized chlorine (isocyanu rate) more effec-tive in an outd oor pool setting than other types ofchlorine?

4. When using bromine as a disinfectant, will the pH ofthe pool water become higher or lower after treat-ment? Explain why and what you would do to coun-teract that effect.

5. Name the two methods of producing ozone.

6. Define pH . How is it measured?

7. What are the effects of low pH pool water? High pH ?

8. When using acids to control pH , what precautionarymeasures should be followed?

9. What d oes a test result of 100 pp m for cyanuric acidindicate? What is th e corrective action, if any?

CHAPTER 3

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Pool Disinfectants and pH