Pool Operations

"Those that go that extra mile go on trips and get bonuses!!"

Pump Operation

Modern-day swimming pool re-circulation systems filter, heat, and chemically treat Pool water before it is re- turned to the pool. Re-circulation system designs have progressed over the years from "fill-draw" and "flow thru" to "open" and "closed' systems. The fill-draw and the flow thru systems are rare and exist only where natural conditions provide unpolluted, clear water.
The open (gutter-to-waste) system may still exist in a few older and larger pools. Water that overflows into the perimeter trough or gutters is wasted. These pools exist under grandfather clauses in many states, but be- cause of increased costs for energy and operation; many are being converted over to a closed system. The closed system returns or retains all swimmer-displaced surplus water within the system and eliminates loss of pool water.

Water Distribution

The modem re-circulation system evenly distributes water throughout the pool to assure balanced water temperatures and chemical effectiveness and to prevent circulation dead spots. Pool circulation patterns begin by equally distributing water as it leaves the pool for re-circulation. Common practice and state codes require that an overflow of 50% or more of the re-circulated water be carried through the skimmer or perimeter overflow through, and 50% or less through the main drain. The design of many systems permits a manual or automatic adjustment in valve clearance or the use of instrumentation to alter this balance. A pool with swimmers in it will produce waves (dynamic surge) sufficient enough to provide adequate skimming of the pool surface. During this period, by increasing the main drain return to 75%, a more active bottom now pattern will occur. This balance permits the lesser debris, hair, and lint to move down the slope of the Pool bottom to the drain, reducing unsightly collections in the deep end and in the corners.
The system for returning re-circulated pool water is designed so that the volume, first, maintains a consistent pool level that Permits effective skimming of oils and floating debris; second, the incoming water produces a now pattern that moves heavier debris or keeps it from settling on the bottom and eliminates dead spots.

Outlets

Water returning to the filters, through perimeter over-flow troughs or skimmer outlets, flows through strainers to trap large floating debris. These strainers must be cleaned periodically to permit efficient return.

An adjustable weir, or gate, moves automatically with the water level to assure constant one way flow of surface water.  Perimeter overflow troughs do this also but skim a greater surface area.  Water level of the pool must provide a continuous overflow to be in compliance with state codes and regulations.
The bottom, or main, drain is an effective outlet that assures that debris settling to the bottom is removed. For safety's sake, care should be taken to ensure that the drain's grate has screws that are tightened so that it cannot be removed by swimmers. Also, the suction should be distributed over a large enough area so that it is not powerful enough to entrap swimmers. Main drains should not be located in line with diving boards, but if so located, the drains should be clearly marked. They must be designed to prevent injury upon impact with the grate.

Inlets

Location of inlets is important in directing the circulation pattern of the pool as well as in equally distributing water, temperature, and chemicals. The movement of swimmers aids circulation in shallow water areas. Deep end circulation, however, relies heavily on the flow pattern established by the inlets in that area. Adjustable inlets for direction of flow and volume are valuable in maintaining an effective circulation pattern. Patterns should move toward the deep end and from the bottom of the pool toward the surface. Circulation dead spots are found in many pools. These areas are generally in corners, on stairs or ledges, along walls, and in the deep end between diving board entry areas. These areas need added attention while brushing and vacuuming.

Recirculation Equipment

The re-circulation system must be designed to have the following capabilities: (1) hold displaced water in reserve, (2) filter, (3) heat, (4) chemically treat and balance, and (5) re-circulate the required volume of water. These design parameters are further influenced by the size of the facility, programming needs, and operational controls. For this reason, many different types of re-circulation equipment have been designed. The general features of each equipment component and a review of their operation follow.

Re-circulation Pump

A PUMP establishes the limits of the volume of water that can be re-circulated. The pump causes water to flow, but it also determines the direction of flow. Pump capacity is calculated in gallons per minute (gpm) or in head, which is expressed in pounds per square inch (psi). It is essential that both dimensions be given any time reference is made to a re-circulation pump's performance. Figure 4.2 illustrates this relationship.
Swimming pool re-circulation systems use centrifugal pumps. (Figure 4.3) As the name implies, centrifugal force accomplishes the pumping action. Water to be pumped flows from the suction side to the center, or eye, of the impeller. The impeller, spinning at high speeds, throws out water from the center along its blades by centrifugal force. As the water leaves the impeller blades, it contains a large amount of energy in the form of velocity. This energy is converted from velocity to pres- sure by passing the water through an area known as a volute. A centrifugal pump has only one moving part, the impeller, and there is no contact between this part and any other part of the pump.

Two types of centrifugal pumps are used for swimming pools.  Self-priming centrifugal pumps can be located above the water level since they have the ability to "lift" water from the pool surface.  Non-self-priming pumps require that the water fill the pumps by gravity and must be located in a dry pit or pump-equipment room located below the normal level of the pool.
Special characteristics of centrifugal pumps should be noted.  When a discharge valve is closed while the pump is operating (zero flow), maximum pressure is produced.  However, the impeller merely churns the liquid within the pump; it does not create destructive pressures such as occur with gear or piston pumps.

  
When the influent pressure decreases, the flow increases.  Conversely, as pressure increases, flow decreases.  Therefore, when a pump is operating with clean filters, it produces greater flow with less influent pressure than when the filters are dirty.  When the pump flow is not regulated with a controller, the flow rate will change during the cycle.
Another important characteristic of centrifugal pumps is that the horsepower consumed increases as the flow produced increases. When a filter is clean, the pump produces a high rate of flow and, therefore, consumes maximum horsepower. As the filter becomes dirty, the flow rate decreases and at the same time the horsepower decreases. The least amount of horsepower is used when the discharge valve is closed completely. There is zero flow and maximum pressure.

It is also interesting to note the effect that changing the speed of operation has on the centrifugal pump's performance. When speed is changed, the flow rate changes in direct proportion to tire speed change. The pressure changes by the square of the change in speed, and the horsepower requirement changes by the cube of the change in speed. For example, if the speed of a pump were changed from 17-50 rpm to 3500 rpm (two times), the flow would double, the pressure would multiply by four, and the horsepower requirement would multiply by eight.

Piping

Formulas have been developed to determine flow rate potentials according to pipe diameter, length, and number of elbows. The larger the diameter, the less friction loss and the less pressure required passing water through the pipe. As a rule of thumb discharge piping should not be sized to exceed a velocity of 8 feet per second, and suction piping not to exceed a velocity of 6 feet per second. Any change in an established system, such as a different pump, or new filters or design, requires new calculations to determine flow rate potentials. Existing systems are designed to function at capacity, and any change usually requires approval from a state or local regulatory agency before it is made.

Hair and Lint Strainers

Pump impellers fit their casings with minimal clearance and must be protected from foreign objects that might upset their balance. Objects, such as hair, hairpins, rubber bands, band-aids, and rubber straps, are large enough to cause harm both to the pump and to the motor if they are not screened out before they reach the pump.
Strainers are usually metal or plastic baskets and are inserted on the suction side of pressure filter systems. They are not practical in vacuum filter systems because the filters will have already screened out all debris. Strainers should be checked daily because they are the first things that affects flow rate. Often objects, such as bathing caps, and plastic bags, can slip through a bottom drain and close off water flow. A visual check of the flow meter can be made before opening up the hair and lint strainer to see if there has been any large change.

Surge Chamber or Balancing Tank

The surge of water displaced by swimmers entering the pool is held in a reservoir or balancing tank. The tank's capacity should be large enough so that the water displaced by an active swimmer (approximately 20-25 gallons per person) will not exceed the tank's capacity and overflow into the sewage system. Holding displaced water in reserve is a cost saving practice. Watch to see whether or not a lot of water is being displaced and is overflowing to waste.
During events, such as swim meets, when high numbers of bathers enter the pool at one time, the pool Overflow return lines should be restricted by throttling 'valves in order to hold the surplus water within the pool. When many bathers enter the pool at the same moment, the amount of water displaced is greater than the capacity of most balancing tanks. The water is wasted unless it is held in reserve in the pool.
Connection to the local water supply must design so that it does not allow pool water to siphon back into the domestic line when make-up water is added. The balancing tank is the best place to introduce make-up water to the pool, and a 6" air gap in it will prevent backflow into domestic water.

Valves

Proper valves in a system permits control of re-circulated water Each piece of re-circulation equipment should have a valve on both the influent and effluent side to permit isolating each individual unit for maintenance by shutting off water flow from both sides. Valve throttling is a popular technique for reducing the flow rate in the entire re-circulation system.  Ball, gate, butterfly, and float valves are commonly used. 

Pressure Gauges

Most re-circulation systems have a pressure gauge on each side of a pressure filter (influent and effluent), or one following the filter, but before the pump, for a vacuum filter. Pressure differences between the two, are an indication of filter efficiency and, when following manufacturer's advice, determine the need for back- washing. The variation of pressure between influent and effluent gauges is unique to each pool's filter system. The interpretation of pressure differences between gauges for each system is based upon the design as well as the recorded experiences (history) of that system.

Flow Meters

Most state codes require the installation of a flow meter with each re-circulation system. A reliable flow meter is important in determining the effectiveness of the re-circulation system and whether or not the system meets regulations for filtration.

A variable area flow rate indicator (Figure 4.8) consists of a vertical glass or plastic tube with a center bore that becomes progressively larger in diameter from bottom to top. A small ball is placed in the tube, and, as the velocity in the channel varies, the level of the ball changes to show the rate of flow. The tube is calibrated in gpm.

Mercury manometers employ a pressure differential principle to indicate flow rate. (Figure 4.9) As the flow rate increases, the pressure differential across an orifice plate changes the level of the mercury column. Supported by the water pressure, variously sized orifice plates allow the flow meter calibration in gallons or liters per minute.

Some unique features of newer flow meters include remote readout (up to 700 feet), analog and digital averaging, display readouts, and meters with computer-compatible electronic signal generation.

Flow Controllers and Flow Switches

Automatic flow controllers are available to regulate and stabilize water flow. These devices read the current flow and, by tensing or relaxing an internal spring assembly, can control the flow at a constant rate within a 5% tolerance. As filters collect solids and debris, the rate of flow tends to decrease. The automatic valve compensates for this decrease by allowing a corresponding increase in valve orifice size, which maintains the flow at the desired rate. Decreasing or increasing the internal resistance against the pump maintains a constant flow.

Measurement of Total Dynamic Head

Measurement of total dynamic head is relatively simple. There may be a vacuum gauge or a manometer on the suction adjacent to the pump and a. pressure gauge adjacent to the pump discharge. If not, they may be- added to a system already in operation. A vacuum gauge reads in inches of mercury and is multiplied by 1.133 to arrive at the total head in feet for the suction side of the system. Multiply the discharge side pressure gauge by 2.31 to find the head in feet on that side. Add both heads together to find the total dynamic head.

Head readings can be calculated during normal filter operation, backwash, or vacuum cleaning. To determine flow rate at various head readings, the calculations should be compared to the system's pump curve that is supplied by the manufacturer.

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Pool Water Testing

 
Regular and precise testing of swimming pool water is essential for maintaining a healthful, clean pool. Performing certain tests assures that Pool water is kept within predetermined standards. Irregular or imprecise testing invites many problems: the pool can become unsafe for swimming; bathers can risk infection; algae can grow, causing the water to look milky, green, or hazy; the pool's bottom and sides can become slippery; improper pH control can reduce the sanitizer's effect on bacteria and can damage the pool's surfaces and circulation system; and too much disinfectant can irritate bathers and damage their bathing suits.

Proper control of all the variables involved in pool chemistry is assured only by constantly monitoring the water, evaluating the findings, and adding chemicals or controlling chemical feeders as necessary to maintain proper balance. The testing procedures involved in these processes have been simplified as a result of the development of kits containing premixed reagents (any sub- stances used in a chemical reaction to detect and measure other substances), prepackaged tablets, and calorimeters to compare results with laboratory color standards.

While water testing has been made simpler through the development of easily used test kits, quality of these test kits varies considerably. A number of companies produce a laboratory-quality kit for more exact chemical readings, but the general-use kits are inexpensive and can be used for spot tests by trained pool personnel. The laboratory-quality kit should be cared for, secured, and used only by a technically trained operator.

Test and control procedures also have been improved through recent development of electronic analyzers that read, evaluate, and adjust the pool water chemistry. The operator need only conduct periodic checks (confidence checks) to insure that the electronic readout agrees with the water tests. The controller does everything else, including turning on pumps and adding the proper chemicals to balance the water chemistry.

Regardless of the system in effect, all operators must follow basic rules when testing water.  Disinterest, sloppy instrument handling, hurried procedures, bad reagents, or inaccurate measurements will ultimately cause problems. The following rules apply to all chemical testing:

Testing for Bacteria

Testing water sanitation requires counting the numbers and types of bacteria present in a sample. Periodic tests are conducted by health agencies, also, to insure that public swimming pools are free of disease-causing organisms.

Testing water for bacteria content is an involved process that cannot be done at poolside. The operator should, however, be familiar with the technique involved. Sterilized bottles are used to collect water sample. Care must be used not to contaminate the sample by touching the inside of the bottle, the bottle top, or inside its neck. The closed bottle is immersed in the water; the top is removed and then replaced while the bottle is still under the water.

The sample must promptly be taken or mailed to a laboratory where two. 24-hour tests are administered. The first is an incubated growth test for a bacteria count, and the second is to assure that the bacteria are harmless.

Most public health agencies test pool water for the presence of coliform bacteria. Finding a high coliform contamination is usually basis for closing a pool until the condition is corrected. Bacteria in swimming pool water are controlled by the proper use of pool sanitizers.

Testing for Chlorine

Simply stated, there are three types of chlorine test readings: free, combined, and total. Free, plus combined equals total.  Only the free chlorine is effective in killing bacteria or algae. The combined chlorine represents a need for more chlorine additions to release it, whereas the total chlorine content as represented by the OTO test could be either free or combined.

OTO Methods of Determining Chlorine Levels

For many years, the most common test for residual chlorine has been the OTO method. It is based on the fact that a clear, organic solution called orthotohdine (OTO) turns yellow in the presence of free or combined chlorine. Increasingly greater concentrations heighten color intensity until a deep orange or red color is reached at extremely high chlorine values.

Free Chlorine Test Using OTO

 Total Chlorine Test Using OTO

Authorities as out-of-date or inferior to DPD testing regard OTO testing, while still used in the United States. In many public health jurisdictions the OTO test has been prohibited.

DPD Methods of Determining Chlorine Levels

The DPD method, using standardized tablet reagents containing diethylphenylene diamine indicators, offers the advantages of reagents that are highly stable and easy to work with. DPD tablet reagents come in foil packets or plastic pillows for easy handling. They have an extended shelf life and produce a color change that is easily discernible. Multi-part liquid DPD reagents are also available.
Separate DPD tablets or liquids are used to test for residual chlorine in its various forms: Free available chlorine, using DPD tablet #1 or liquid reagents #1 and #2; total available chlorine, using tablets #1 and #3 or Liquids # 1, #2 and #3; and combined chlorine or chloramines, subtracting the free reading from the total. Other tablet numbers are normally not used in pools.  Number 2 is used for monochloramine, and #4 measures total chlorine only.

Free Available Chlorine Test Using DPD Tablets

Test kits with precise liquid standards, closely graduated, are available. Some kits use clear water vials next to the test vial to make the optical light paths similar when judging color standards to the chemical readout.

Total Chlorine Value Test Using DPD Tablets

Combined Chlorine Calculation

Calculate the combined available chlorine (chloramines) value by subtracting the free available chlorine residual value reading from the total available chlorine residual value reading.

Testing for pH Values

pH of water is determined by adding an organic dye to the sample at a measured rate. Dyes to cover the entire pH range of 1.0 to 14.0 are available. Because most pools are kept in a pH range of 72-7.6, the pH test that uses a reagent is particularly effective (pH range of 6.8-8.2). Testing procedures are similar to testing chlorine. A phenol red tablet is added to the vial of pool water and measured against a color comparator in the pH test kit. At the low end, the sample is yellow, developing an increasingly red color as the pH increases.

Some days are subject to bleaching by chlorine others react with the chlorine to form new compounds that can give false readings. Adding a small quantity of sodium thiosulfate should neutralize bleaching action. (Some indicator solutions sold specifically for pools already contain sodium thiosulfate to combat this bleaching action.)

Tablet Method for Testing for pH Level

Solution Method for Testing for pH Value

Testing for Hardness

If in excess, hardness (a measure of calcium and magnesium in the water) causes calcium scale formations on plaster pool walls and in heater elements. Scaling may be accelerated in pool systems that require the frequent addition of make-up water as a result of evaporation or that use calcium hypochlorite as a bactericide. This is especially true if the make-up water is moderately or excessively hard.

To control scaling, pool water that exceeds 800 to 1000ppm hardness should be diluted or replaced with water of substantially lower hardness or that has been partially softened.  With excessively hard water, lower ph values should be considered.  A careful calculation of the water's calcium saturation index (Langelier) allows one to choose pH and total alkalinity values in order to keep hard water from causing scale. For example, at 500 ppm calcium hardness and at a 100 ppm total alkalinity. A pH of 7.3 is in order, while even 7.2 is acceptable.

If hardness is too low, aggressive water results. This allows corrosion and calcium (plaster) degradation to occur if high pH values are not held to offset the resulting negative calcium balance. Holding high pH values is a poor way to offset low hardness, since chlorine effectiveness suffers greatly. Calcium chloride should be added to establish more normal calcium hardness levels.

Hardness is the measurement of the mineral content of water. Total hardness- and calcium hardness can be determined independently, as described below. The calcium content is often 65% to 75% of total, with the remainder primarily magnesium. Calcium hardness is. By far, the most important consideration in pool water mineral content.

Calcium Hardness Test

Calcium hardness can be approximated be taking 70". of the total hardness results. However, more accurate measurements can be made be using a test kit designed specifically to determine calcium hardness and be following the manufacturer's directions regarding color changes.
In these tests, too, a specific amount of water is taken from the pool, and an indicator is added to the sample. A reagent is added, causing a color change that indicates the amount of calcium hardness in the water.

Total Hardness Test

To test for total hardness, an exact amount of pool water usually 60 ml) is treated with a solution called a buffer. Then a dye is added. The reagent is added to the sample and mixed. one drop at a time. The number of drops necessary to change the watercolor, multiplied by a constant provided be the test kit manufacturer. Determines the hardness in parts per million.

The tablet method for testing water hardness is equally simple. A tablet containing the pH buffer. the indicator dye, and the hardness reagent are added to a 100 ml sample of water. The color changes as additional tablets are added. The number of tablets required to bring about this change is recorded and multiplied be reading per tablet as provided by the test kit manufacturer.

Testing for Total Alkalinity

Testing for total alkalinity is essential in order to make proper determinations of the calcium saturation index as well as for bather comfort and ease of pH control.

A pool's total alkalinity (calcium carbonate) may be determined through use of many commercially available test kits.  A quantity of pool water is mixed with an indicator; a blue color reveals the presence of alkalinity. Sulfuric acid is added to this mixture from a dropper. The operator counts the number of drops necessary to neutralize the alkalinity and bring about a color change to red. Alkalinity can be determined by multiplying the number of drops used by a constant as provided be the test kit manufacturer (usually I drop = 10 ppm).

The tablet methods are available for determining alkalinity, too. Although less accurate than the titration method, the. process is. easy to follow and is less susceptible to error. Tablets are added one at a time until the desired color change takes place. When sufficient tablets have been added to bring about the end-point color change, the number of tablets required is multiplied be the reading per tablet as provided in the manufacturers tables.

Testing for Cyanuric Acid (ISOCYANURATES)

Cyanuric acid is a common additive that stabilizes chlorine, values in residential and small commercial swimming pools, and, to a lesser extent, in larger pools. If not carefully monitored, however, the concentration can increase to a point that the chlorine is over stabilizing and rendered ineffective. Dilution is the only wav to reduce isocyanurate levels. Often one-half the pool or more is drained and replaced to reduce concentrations when so called stabilized chlorine compounds are used exclusively. As the oxidant, and their built-in cyanuric acid builds up to excessive levels. It is almost impossible to completely eliminate, even after repeated draining of the pool.

The acceptable range of Cyanuric acid is generally between 20 ppm and 100 ppm. Cyanuric acid levels below .5 ppm substantially reduce the desired stabilizing property; most health departments prohibit levels above 100 ppm.   Ideally, stabilizer residual should not exceed 20 to 30 ppm in heavily used high-volume, outdoor public pools.

One test for the cynuric acid value requires mixing equal parts of pool water with a standardized melamine solution. The resulting cloudiness provides an indication of the water's cyatiuric acid concentration. Finally graded particles give the water a hazy appearance, which indicates a low concentration. Larger particles give the water a milky appearance, which indicates a high concentration.

A dip rod with a black dot on it is submersed progressively deeper while the observer looks down through the solution.  When the dot disappears, the isoyanurate concentration is read on a graduated scale etched on the rod.

Other cyanuric acid tests use tablets and comparators or more concentrated reagents. All, however, are based on the turbidity (milkiness), and none are accurate below 15 ppm or above 80.
Needs must be considered carefully and the ramifications studied before using cyanuric acid, especially on large, automated pools. The stabilization, while making chlorine last longer, substantially reduces its oxidation potential. This oxidation potential, the qualitative mea- sure of chlorine's work value, is what most automation devices control; therefore, calibration of instrumentation will shift. Consistent, accurate control, although possible, becomes more difficult for the operator.

Testing for Copper

Copper in low concentration can be measured with simple test kits. Most require the addition of two re- agents to the sample, and produce a blue or green color in the presence of copper. The color is then compared with the kit's prepared color standards. Laboratory procedures are necessary to obtain accurate determinations, especially if excessive metal compounds are present.

Testing for Iron

Iron in low concentration also can be measured with readily available test kits two reagents are used; a blue color appears if iron is present. The water sample is then compared with the color standards in the kit to deter- mine the iron concentration.

Prepackaged Test Strips

A recently marketed method for determining chlorine levels and pH values, etc., uses prepackaged test strips. Each strip usually permits tests for pH, residual chlorine, total alkalinity, and calcium hardness by providing separate pads containing reagents that react with the pool water. These pads are compared to a color standard, often printed on the bottle label. These test stripes are a good guide, but should not be relied upon or close tolerance accuracy.

Summary

A property maintained pool always looks clear, has a blue shimmer to it (never any indication of green), and is properly balanced to maintain good swimming-quality water. The trained Certified Pool/Spa Operator (CPO) through intelligent use of swimming pool chemicals systems, and the efficient use of energy accomplish this at times.

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Chlorination

This is the most commonly used method of sanitization today. Bromine and iodine are other members of the halogen family of chemicals also used to sanitize water. Other chemicals include ozone, silver, and copper com- pounds. Ultraviolet light is a non-chemical disinfectant. Each of these methods will be covered to some extent, but chlorination is presently the most widely accepted means of treating pool water.

While there are many chlorinating agents (or sources of chlorine), the active chemical that is always formed when each is added to water is hypochlorous acid. (HOCI). Since each chlorinating agent gives the same active form (HOCI), we can ignore the source for now and deal with the process of chlorination, in general. Hypochlorous acid (HOCI) is an extremely active, powerful chemical. It not only destroys  'such harmful organisms as bacteria, algae, fungi, viruses, etc., it also destroys impurities that are not removed by filtration. These two processes are called sanitization and oxidation.

As mentioned, hypochlorous acid is the form of chlorine that provides sanitation. It is often referred to as free available chlorine (FAC). Because it is an extremely active chemical, however, it also reacts with organic impurities. When there is enough HOCI present, the impurities are completely oxidized. Combined available chlorine (CAC) is formed when there is an insufficient supply of HOCI, or when there is a very heavy load of impurities. Combined chlorines result when impurities are only partially oxidized but can be destroyed by increasing the HOCI supply. This is called, breakpoint chlorination.

Finally hypochlorous acid is affected by the pH, or acidity, of the water, and by ultraviolet radiation or sunlight.  The effects of pH and the sunlight stabilization of HOCI will be covered is some detail here as will each of the topics mentioned above.  Methods for testing free and combined available chlorine pH and the other water parameter are discussed in the chapters on testing.

Sanitization is the process of destroying organisms that are harmful to people. These organisms, referred to as pathogens, more commonly are called germs and include bacteria, fungi, viruses, etc. Chlorination also controls algae (which are not usually harmful them selves, but the conditions that allow algae to grow also foster the growth for bacteria). In addition to being unsightly, algae can cause the surfaces around the pool to become slippery and unsafe.

While each of these organisms may require different amounts of hypochlorous acid for control (ranging from a few tenths to several ppm), the required amount for public swimming pools is often established by local health officials. Very often local codes will specify 1.0- 1.5 ppm but some might vary from this.
Part per million (ppm) is a term used to express very low concentrations. Higher concentrations are usually given in percentages (%) meaning parts per hundred, so that 10',16 available chlorine in sodium hypochloritc- solutions means that there are 10 parts of chlorine per hundred. or one part in ten. For example, a gallon of liquid pool bleach weighs about 10 lbs. The amount of available chlorine in that gallon is therefore one pound. To get-a feeling of the low concentration term of ppms, imagine trying to find one particular penny in a bag containing 510,000 in pennies. One part per million of available chlorine (AvCl) is so powerful that it is like having one policeman patrolling a major city of a million people by himself to keep it safe.

Oxidation is the process of chemically removing organic debris, such as body oil, suntan lotions, and perspiration. from the water. The process is similar to burning trash in air. It is not important to understand the chemistry involved; it is sufficient to know that enough chlorine in water will chemically "burn" impurities.

The use of chlorine to clean up water is a supplement filtration, discussed in another chapter. Filters remove the dirt and debris suspended in water, but even the best filter cannot remove dissolved impurities since they are not physically separate from the water. If the water looks dull or hazy, even though the filter system is operating properly, the operator should consider a chlorine shock treatment to oxidize the dissolved organic impurities and restore the clarity of the water.

Shock- treatment and super chlorination are terms describing an extra large dose (usually .5 to 10 ppm) of chlorine to remove dissolved filth or visible algae from the water. This is the same as using three to six times the normal dosage of a chlorinating agent. For example, a 50,000-gallon pool requires about four gallons of liquid pool bleach (10-AVCI) or six pounds of a solid such as calcium hypochlorite (65%AvCI)
Algae are actually simple plants that live in water.  Although there are actually many different kinds, there are three general varieties, usually referred to by their colors: green, black, and yellow. The most common, that- free-flotation green algae, is also the easiest to control by shock treatment since it is usually suspended in the water. Black and.yellow algae normally attach them selves to surfaces such as walls, floors or steps. Affected surfaces should be brushed three or four times daily to remove the algae. Repeated shock treatments may be required in some cases, based on the chlorine levels.

Combined chlorines are formed by incomplete oxidation of nitrogen containing impurities. Perspiration and urine contain ammonia, but even a swimmer's skin and body oils contain proteins that form combined chlorines or chloramines. In order for combined chlorine to be of available to be of any use against bacteria, it still must be "available." When compounds, such as chloramines or other products similar to the chlorides are formed, the chlorine is no longer available and is useless for sanitization. Free available chlorine and combined available chlorine exist together in many pools. Simple tests, described in another chapter, measure the amounts of each that are present in a pool.

In addition to reduced effectiveness an anti bacteria, chloramines cause eye irritation and the so-called chlorine odor that swimmers complain about. Chloramines have a foul, irritating odor, unlike the fresh-laundry-like odor of high free-chlorine residuals.

Breakpoint Chlorination

When chloramines are known to be present either by test (over 0.2 ppm CAC) or because of a foul chlorine odor, the continued addition of chlorine causes a corresponding rise in residual, but eventually a point is reached at which addition of chlorine causes a sudden drop in residual. This phenomenon is accompanied by a reduction in eye irritation and chlorine odor.

Investigation reveals that when the residual concentration of chlorine reaches the proper level, the oxidation of these chloramines and other products suddenly goes to completion, eliminating them entirely. The point of residual concentration at which this sudden reaction occurs is called the breakpoint. Chlorine remaining, or added after the breakpoint is reached, exists as free residual chlorine, and all the combined residual is lost. The break point varies in its speed and amplitude, depending upon the organic matter present. In some waters, the breakpoint is hardly discernible.

The practice of periodic super chlorination is actually an attempt to pass the break point in order to rid the water of an accumulation of combined chlorine residual and potential chlorine-consuming compounds.

Effect of pH on Chlorine

The acidity of water has a definite effect on the efficiency of chlorine as well as on the corrosive properties of water. It can be seen in table 5.1 that free chlorine is most efficient in the lower pH ranges. Some operators do, however, maintain higher pH conditions in the pool. They should also maintain appropriately higher free available chlorine levels in order to provide the same concentration of the active HOCI form.

For example, it requires 2.5 ppm free available chlorine (FAC) at pH = 8.0 to provide the same amount of HOCI (0.5 ppm) as when there is 1.0 ppm FAC at pH = 75. For this reason, many authorities recommend that the pH of pools be maintained in the range between 72 and 7.8 and as close to 7.5 as practical. These conditions are also considered to be most comfortable for the swimmer's eyes and skin. 

Chlorine Gas (CL2)

Chlorine gas at 100% available strength, is very toxic, and can be lethal if an operator is overcome by it. This form of chlorine is the most economical, pound for pound, but the laws regarding safety practices and the intricate feeding equipment it requires make it the most expensive method of water sanitization. Chlorine gas for pool use is contained under pressure in steel tanks as large as one-half ton. The gas is green in color and heavier than air.

Strict adherence to the following practices is required for minimum safety.

Sodium Hypo chlorite (NaOCI)

Sodium hypochlorite is a clear, slightly yellow liquid solution used in dilute form as common household bleach. In its commercial form it contains 10% to 15% available chlorine. The chemical is usually introduced to pool water through a chemical feeder, but it can be poured directly into the pool for a quick increase in chlorine residual. It has no-sediment or precipitate. This chemical has a pH of 13 and causes a significant increase in the pool's pH. The occasional addition of muriatic acid can correct the increased pH, however.

Sodium hypochlorite is not stable in storage and gradually loses strength, especially in sunlight. If stored in a dark, cool room, it has a one-month shelf life.

Dilute solutions of sodium hypo chlorite can be used for poolside sanitation and for disinfecting and cleaning decks. The chemical should not be spilled directly on clothes and should be immediately washed off if it get-, on the skin. However, its safety and low cost has made this chlorinating agent popular for small pools and residential pools.

Calcium Hypachlorite (Ca (OCI)2)

Calcium hypo chlorite is available in granular or tablet form. It contains 65"n available chlorine by weight and remains stable if stored in a dry, cool area. The chemical can be dissolved and introduced to the pool as a liquid. or it can be added in dry form by hand. When applied directly to the pool, it may cause a temporary, cloudiness. Direct applications should be broadcast evenly over the water surface to avoid bleaching the pool bottom as a result of having a concentrated amount in one spot. This must be done when no bathers are in the pool.

This chemical, when contaminated likely or mixed with an organic compound, can produce a fire. A good rule is never to mix calcium hypo chlorite with another chemical or store it in anything but the original container. Mix the chemical into water not water into the chemical. Calcium hypo chlorite should not be handled with bare hands and must be kept off the operator's clothes.

As a chlorinating agent, calcium hypo chlorite will slightly increase pool pH. It has a pH of II.S. Operators of gas chlorinated pools often keep a supply on hand for emergency use or for a quick charge when super chlorinating. In its liquid form, it can be used as a sanitizing agent for decks and locker rooms.

Lithium Hypo chlorite (LIOCI)

Lithium hypo chlorite is a recent entry in the field of chlorinating agents. Its cost is greater than other hypo chlorites, and it yields only about 35% available chlorine. However, the chemical is totally soluble in water, and pH tends to rise more slowly with its use than with other chemicals. Precautions to observe are similar to those when using calcium hypo chlorite.

Chlorinated lsocyanurates (Stabilizers)

This family of chemicals is in wide use for swimming Pool chlorination. The family is composed of sodium dichloro-isocyanurate and trichloroisocyanurate acid. The sodium compound is the soluble of the two and contains between 56% to 62% available chlorine.  Trichloro-isocyanuric acid has 89% available chlorine and is used when the slow release of chlorine over a period of time is desired. The sodium compound has little effect on pH, while trichloro is slightly acid. The sodium compound can be added directly to the pool; trichloro is generally fed through an erosion-type feeder.

The effect of stabilization on hypochlorous acid (HOCI) is two-fold. First, HOCI is readily decomposed by ultraviolet radiation, such as contained in sunlight. For this reason, the dosage of a chlorinating agent that is sufficient for an indoor pool is dissipated rapidly in an outdoor pool. A stabilizer combines with the available chlorine in a manner that does not consume it. Secondly, by combining with the free available chlorine, stabilizers generally tend to reduce its efficacy, especially at low concentrations.

In recent years, stabilizers have been introduced with varying results. The most recent one, cyanuric acid, seems to be winning considerable acceptance due to its ability to release chlorine as needed, yet prevent its dissipation by sunlight. Studies have shown that cyanuric acid impairs the rate of kill of chlorine when tested under laboratory conditions, but shows not much slowing action in tests with actual pool water. In one such test in which chloramines was present in the pool water, the presence of cyanuric acid actually produced a faster kill than the chloramines alone.

While the sunlight-stabihzing effect cyanuric acid on hypochlorous acid has been clearly shown, there is no general agreement on the issue of whether or not there is a significant reduction of F.AC efficacy by cyanuric acid. The pool operator should consult the local codes on the proper use of stabilizers.

Chlorination Summary

Chlorination both sanitizes and cleans the water by oxidizing organic impurities.
A free chlorine residual Of 1.0-1.5 ppm is preferred. Combined chlorines should not exceed 02 ppm and may be destroyed by breakpoint chlorination.

Proper pH control (7.2-7.8) provides better chlorine efficiency.

When stabilization by an organic acid is allowed for outdoor pools, reducing the chlorine demand due to sunlight reduces chlorine consumption.

There are many chlorinating agents available but each provides hypochlorous acid, the active chemical specifically for disinfection's.

Other Pool Sanitizers

Other members of the halogen family, bromine and iodine, are used for treating pool water.  New developments in the use of ozone, ultraviolet light, ionization of salts, and other chemical compounds continue to provide new challenges and techniques in water treatment.

Bromine

Bromine is available in liquid or solid. In liquid form, it is heavy, dark brown, and volatile. Its fumes are toxic and irritating to eyes and respiratory tract. In its solid form, a "stick" of it is allowed to dissolve slowly in the recirculation system, making it safer to handle than the liquid.

The chemistry of bromine is similar in many respects to the chemistry of chlorine; however, bromine is not as effective in oxidizing organic matter or algae. Its oxidative action in the presence of ammonia completely destroys the ammonia when hypobromous acid (HOBR) is in excess. When less hypobromous acid is available, the mono and dibromaniines are still highly effective bactericides and are less irritating to swimmers' eyes and skin.

Iodine

Potassium iodine is a white, crystalline chemical that dissolves in water without a precipitate.  It must be converted to iodine by use of an oxidizer such as hypo chlorite.  Iodine does not react with ammonia to produce indamines; it does not bleach hair or swimming suits and eye irritation is practically nonexistent.
Other chemicals (usually chlorine) must be used in conjunction with iodine to control algae and oxidize organic matter.  Its sole effect is to produce bacteria-free water.  Iodine affects metals and produces green-colored pool water.

Ozone

Ozone is an effective germicide with a 50% greater oxidizing potential than chlorine.  It is a gas and in most states the equipment and method for its use are classified as auxiliary and are designed to work in conjunction with conventional chemicals.  Ozone is more active than most commonly used pool chemicals in oxidizing organic matter and bacteria.  It produces no chemical residuals any unconsumed ozone reverts to pure oxygen.  It does not alter the water's pH.

Ozone provides improved particle coagulation in spa water that has increased chemical demand because of high water temperatures, excessive aeration, and heavy bather water ratio.  No changes in rate of introduction are necessary; an ozone system works continuously with the operation of the filtration system.  Ozone has a mild chemical odor, and can cause mild eye, nose, or skin irritation.

Ultraviolet

Ultraviolet radiation has been used as a bactericide in public water supplies for many years. It causes none of the chemical complications that are common with chemical additives; however, water turbidity reduces its effectiveness by screening the rays. The greatest deterrent to its use for swimming pools is the requirement in aft states that a bactericidal residual be maintained. Radiation technique is effective only with direct application on the water passing by and produces no residual effect to neutralize bacteria brought into the pool by other means.

Silver

The bactericidal properties of silver nitrate and argenol are well known in medical practice. Silver ions are introduced to water by electrolysis or by passing a current through a silver electrode. The primary limiting factors in its use in swimming pools are the high cost of silver and the fact that its bactericidal action is quite slow.

Electrolytic Cells

Electrical devices (chlorine generators) have been developed that produce chlorine from the natural or added wait within pool water or within the machine. This method is becoming popular in Holland and other European countries. Because of their use on spacecraft, development of metals that are used for electrodes has been rapid. There is a real future for this concept in sanitizing water.

Other Pool Chemicals

The greatest use of chemical products is in the bactericidal treatment of pool water. Many special conditions however, create requirements for additional chemical treatment.

Flocculants

Aluminum sulfate (Al2(SO) is used as a filter aid and as a coagulant and settling agent for water turbidity.

Alum "floc" is a white, gelatinous substance that attaches to free-floating matter in water to form larger heavier-than-water particles, which settle to the bottom of the pool.  Alum floc is especially effective on sand filter beds. The floc partially fills the voids in the sand bed and holds organic debris in its suspended gelatinous coating.

Aluminum sulfate is introduced as a filtering aids at the most convenient entry point ahead of the filter. The chemical feed, hair and lint strainer, or skimmers are effective points of introduction. However, to coagulate particles in pool water, a powered alum is broadcast over the pool surface and permitted to stand overnight or for a minimum of two hours of no use. After standing, the pool should be vacuumed with minimal agitation to prevent the floe from becoming diffused. T%%-,) ounces of powdered alum per 100 square feet of surface area is recommended, but this amount can be adjusted according to conditions.
Flocculent aids, with a combination of ingredients, sold under various trade names, have been used to pro- duce a heavier or more stable floe. Colloidal silica, a clay called detonate, and a new family of organic polvelec- troloytes are available.

Algaecides

The chemistry of algaecides is complex because 46 species of clean-water algae exist. Some algaecides work better on one kind of algae than on another.

A planktonic clean-water alga floats on the surface. Other types attach themselves to rough spots on the floor and walls of the pool and are very difficult to remove. Clean-water algae may be blue-green, red, brown, or black and can cause tastes. Odors, turbidity, slippery spots, as well as increased chlorine demand.

Sunlight, temperature, pH, bacteria, chlorine residual, and the mineral content of the water affect the, presence and growth rate of algae. Algae can be introduced to a pool by wind-borne debris, rain, and failing leaves, or it may be present in the source from which the pool is filled.
Preventing algae growth by chlorination is usually not a problem, but removing existing algae from a pool can be difficult. If algae gets a firm start on the side or bottom of a pool, (Training the pool is sometimes more practical if the local water table is not too high to allow it. The pool should be thoroughly washed down with a dilute muriatic acid or hypochliorite solution. (Note: Structural damage can occur in regions with high ground- water tables).

Sunlight is necessary to the growth of algae, so it is a much greater problem in outdoor pools. If not controlled, algae can spread rapidly, turning an entire pool dark green in as little as a day or two.

Algae seldom trouble pools that consistently maintain a high free-chlorine residual concentration.  Maintaining free available chlorine and super chlorinating are the best preventive measures.  Combined chlorine is not as effective as free chlorine in preventing algae growth, and bromine and iodine are even less effective.

Algae inhibitor is a commercial product that acts as a penetrating or wetting agent to allow the chlorine to be more effective. Algae inhibitor is said to control all types of algae growth and provide a stable back-up system to chlorine. It is not pH sensitive, does not evaporate, doubles activity with each 20' centigrade rise in water temperature, concentrates on surfaces, and Ls a powerful wetting agent.

Sequestering Agents

Many stains around main drains and inlets have to be, cleaned by hand, but they can be kept from returning. Sequestering agents' increase the ability of water to hold minerals in solution instead of precipitating out to form - stains. Pools with high iron content use a sequestering agent as part of routine pool water treatment.

Degreasers

There are commercial acids and biodegradable deter- gents that effectively clean D.E. filter bags and filter sand. Each product has its own ability to degrease and rejuvenate filters. Each filter system has its own individual solution for doing the job.

Defamers

Foam or suds is a chronic problem for most spa pools. Occasionally, a box of detergent is thrown into the pool as a prank, and a surfactant or wetting agent made specifically for pools is necessary to deform the water. A bottle of de-foamer is handy to have on hand as a safeguard.

Water Saturation (WATER BALANCING)

Water follows certain natural laws just like other thing around us. Unsupported objects fall to the ground, and this is called the law of gravity it is the nature of water to dissolve the things it contacts until it becomes saturated. It is possible for it to dissolve too much and become over saturated, and then water loses its excess material by precipitation. This is governed by the laws of chemical equilibrium, more commonly referred to as water balance.

Many operators are already familiar with this subject to some degree. A commonly used tool in determining the degree of saturation in pool water is the Langelier saturation Index. Originally devised for the more complicated and variable conditions found in industrial water treatment (boilers, cooling towers, heat exchangers, ate.), it has been simplified for use with swimming pool water. The degree of saturation by calcium carbonate (CaCO,) is determined by the pH, temperature, total alkalinity, and calcium hardness found in the pool water. Each of these is explained as well as how it affects saturation and how it can be adjusted.

The pH reading is used directly. The temperature factor (TF), alkalinity factor (AF), and calcium factor (CF) are read from Table 5.2 using the test values obtained from a pool test kit. (See Chapter6 for more on testing).

The constant (12.1) includes a factor for total dissolved solids (TDS), assuming a value of less than 1,000 ppm TDS, When the TDS is found to be higher (1000- 2000 ppm) a value of 12.2 should be used for the constant factor.

In order to determine whether the pool water is saturated, aggressive (under-saturated) or scale forming (over saturated), the operator would (1) complete the water testing, (2) get the correct factors from the table above, and (3) add them up as shown in the following examples:

Calcium Carbonate

Calcium carbonate is a mineral found in almost all natural waters and in pools.  It is the least soluble common mineral found and therefore the one that becomes under or over saturated.

Under saturated water becomes aggressive or corrosive.  It attacks such pool surfaces as walls. Plumbing and equipment.  Plaster walls and tile grout contain various calcium minerals and are the first things attacked resulting in pitting and loose tiles.  Next , metal components such as copper and steel are corroded.  This causes brown or black staining and, ultimately, failure of the metal part.
Over saturated water will precipitate calcium carbonate.  Most often this causes cloudy looking water, but a good filter system removes the precipitate.  Sometimes the mineral is deposited directly over parts of the pool as scale, resulting in rough surfaces or plugged pipes.

Water that is just saturated with calcium carbonate has no tendency to corrode or scale.  This is primarily the meaning of balanced water.

Temperature affects the saturation of water by calcium carbonate in an unusual manner.  Normally, one expect to increase or speed up the solubility of a material by using hot water.  Sugar, for example, dissolves faster in hot coffee than in iced tea.  Calcium carbonate is not only one of the least soluble minerals, it becomes even less soluble at higher temperatures.

Since the temperature of pool water results from seasonal weather conditions or is selected to provide bather comfort, operators cannot adjust it to achieve saturation or balanced water.  They must, however allow for it as shown in the Langelier Saturation Index.

Understanding pH

PH is a number between 1 and 14 that indicates how acid or basic a solution is.  Pure distilled water has a pH of 7.0 and is neither acid nor basic.  Water with a pH of less than 7.0 is said to be acidic, and the smaller the number the more acid the water is.  On the other hand water with a pH of greater than 7.0 is basic and the larger the number the more basic the water.

Acid compounds such as sodium sulfate or muratic acid, lower the pH of water.  Alkaline compounds such as soda ash or sodium hydroxide raise the pH of water.  Alkaline compounds are, they're for basic.  The use of both alkaline and basic to refer to high pH and to compounds that raise the pH, causes some confusion with the alkalinity of water.  The difference between alkalinity and pH is discussed later.
In addition to the effects of pH on the chlorination process, there is also an effect on the total alkalinity of water.  This plays a major role in the degree of calcium carbonate saturation.  This dual effect makes the control of pH very important to the pool operator.

Molecules of water and other substances brake up into electrically charged particles called ions.  Water separates into positively charges hydrogen atoms, called hydrogen ions, and negatively charged particles containing one hydrogen atom and one oxygen atom.

The pH of a solution does not indicate the total amount of an acid or basic in the solution, but only how much of it is ionized.  This point is very important in the subject of total alkalinity, which is explained further on in this chapter.

Control of pH

Accurate control of the pH of swimming pool water is essential. The effects of pH upon flocculants, bacteria- resides, algae growth, equipment maintenance, and bather comfort will be discussed throughout the Handbook.

no pH of swimming pool water must be kept slightly above 7.0 and never exceed 78. Most state health depart- merits recommend that the pH of swimming pool water be kept between 72 and 76. This range provides the best conditions for precipitation of flocculants on conventional 'sand filters and for effectiveness of chlorine as a bactericide.

Corrosive damage to pipes, filters, and pumps might result from operation at a pH below 70. High pH values cause reduced effectiveness of bactericides and encourage the growth of algae.

Control of pH Ls relatively simple. pH can be raised by the addition of soda ash (sodium carbonate, N&,CO,). The carbonate ion produced by soda ash, combines with some of the hydrogen ions and reduces the hydrogen ion concentration. This makes the water more basic. Other compounds, such as sodium hydroxide, can be used, but they are more dangerous to handle and are not recommended. Soda ash can -be added to a pool by dissolving the powder in water and feeding the solution through a chemical feeder, or it can be dissolved -in a bucket and poured directly into the pool water. The amount required varies greatly from pool to pool, and only trial and error experience determines the correct amount for any specific pool.

Addition of acids, or acid salts, causes an increase in hydrogen ion concentration and lowers the pH. Sodium bisulfate (LNaffSO,) is -,in acid salt that is frequently used because it is safe tA) handle. It can be added bevy chemical feeder or by dissolving in a bucket and pouring directly into the pool. Muriatic acid is the commercial grade of hydrochloric acid ([iCI). If the pool operator is sufficiently aware of the dangers and precautions of handling acids, either of these two can be poured directly into the pool when no one is swimming. Acids may also affect the total alkalinity of water. This is discussed in the section on "Control of Total Alkalinity".

Total alkalinity is a measure of the pH buffering capacity, or the water to a change in pH.  This ability to resist change in pH is due primarily to the presence of the family of carbonate ions, but certain other compounds also provide buffering.

The carbonate ions have a special role in water saturation chemistry. The operator must control both the amount of carbonate alkalinity and the pH to provide enough calcium carbonate to saturate the water without having so much that scale forms. Total alkalinity and pH are related in water saturation (or balance) since, at low pH (acidic) conditions, all of the carbonate ions are converted to bicarbonate. There is no calcium carbonate formed and water becomes aggressive to the pool walls and equipment. At high pH (basic) conditions, too much carbonate  formed, and even the smallest amount of calcium ion present precipitates, causing cloudy water or scale. At normal pool pH conditions (7.2-78), most of the carbonate ions are in the bicarbonate form to provide buffering. Small amounts of carbonate ion are present to provide calcium carbonate saturation. Total alkalinity Ls measured with a pool test kit, and, for all practical purposes, is equal to the carbonate alkalinity. Total alkalinity may he used directly to get the alkalinity factor (Alo for the Langelier Saturation Index. A possible exception is when the total alkalinity of the pool water is less than 80ppin and cyanurate (pool stabilizer) is other 60ppm. If both these conditions exist, the operator should determine the carbonate alkalinity (CA) by subtracting on"hird of the eyanuric acid (stabilizer) level from the total alkalinity. If, for example, the operator finds a total alkalinity (TA) result of 75 ppm and a stabilizer or eyanuric acid (CyA) level of 90 ppm, before calculating the saturated index the followed correction should be performed.

The alkalinity factor from Table 5.2 will be 1.7 (at 45 ppm) riot 1.9 (at 7,-) ppm), If these conditions existed for pool #2 in the examples given earlier, the water would be very aggressive (Si = - 0.6 instead of the - 0.4 shown), and the operator should take corrective action immediately to avoid cor- rosion damage to the pool and equipment.

At normal-to-high total alkalinity there should be no need for a correction, and the total alkalinity test result. can be used both as a measure of the pH buffering and the carbonate alkalinity in (ietf-rinining the degree of saturation.

Control of Total Alkalinity

The addition of sodium carbonate ( soda ash ) to pool water causes an increase in total alkalinity because the carbonate ion take some of the hydrogen ions from the solution to form bicarbonate.  However, the addition of sodium bicarbonate ( baking soda) raises the total alkalinity of the water, but does not change the pH by much.

When the total alkalinity of water is low a small amount of acid or soda ash will cause a large variation in pH and the control of pH will be very difficult.

It is essential to maintain a total alkalinity of 80 to 100 ppm in swimming pools to maintain a stable pH.

Total alkalinity over 200 ppm may cause problems depending on the nature of the alkalinity.

To avoid damage to pool walls, dilute muratic acid by adding one quart of the acid (or one pound of sodium bisulfate ) slowly to the gallon of water.  Safety first always add acid to waater not water to acid!!!

Standing in one place at the deep end of the pool, pour the diluted acid in a circular fashion.  Try to reach out as far as possible and pour it close to the surface to avoid splashing it on skin and clothing.

If the total alkalinity is very high, carbon dioxide gas bubbles may be seen rising to the surface.  Repeat the procedure daily until the desired total alkalinity is reached.

When the operator adds acid evenly over the surface by walking it around the pool or injecting it slowly with a feeder pump, the water should not drop below pH locally.  There will be a slight shift in the amount of carbonate ions, forming more bicarbonate ions and some carbonic acid.  There will also be more hydrogen ions present, resulting in a lower pH when this water is mixed with the rest of the pool water.  If the pH does not go low enough to form a lot of carbonic acid, no carbon dioxide gas will escape, and the total alkalinity will remain almost unchanged.

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