Swimming pool sanitation

Swimming pool sanitation refers to both visual clarity and levels of microflora, such as bacteria and viruses in swimming pools. The goal of sanitation is to prevent the spread of diseases and pathogens between users. Unsanitized water may also support the growth of algae which will present as a greenish tinge initially, then if left unchecked may completely inhabit the pool water displaying a solid green murky appearance. A rule of thumb is that the water should be sufficiently clear to permit the main drain to be clearly visible from the pool deck at all distances up to ten meters (eleven yards) in a horizontal direction from the projection of the drain on the pool surface. This however, is merely to be considered a negative indicator, not a guarantee that the pool water is properly sanitized. Swimming pool water can still be contaminated with microscopic organisms, even though it is visually clear. United States Environmental Protection Agency therefore issued the recreational water standards, a few years ago, to restrain the bacterial problem. With the similar objective as of EPA, International Organization for Standardization published the standards of ISO 15553 recently.

Only pools and spas that contain filtrated and disinfected water can be considered safe places to swim. Poor pool maintenance may lead to low levels of disinfectants and clogged filters that may place swimmers at risk for diseases and infections. only way to ensure proper sanitation is to test the swimming pool water with a pool water test kit and fresh reagents.

Water pump
An electrically operated water pump is the prime motivator in recirculating the water from the pool, pressurized at up to 15 psi (1 atmosphere or 100 kilopascals) through the filtration unit, and returning the filtered water to the pool. A typical pool pump will consume 750 watts to 1.5 Kilowatts (3/4 to 1-1/2 horsepower) and will be utilized for 12 hours per day in summer months. Some pool pumps have two motor speeds to reduce power consumption at times when full power is not needed. Other pump manufacturers (typically Italian or other European) have redesigned their units to use a smaller electric motor with heavier windings, therefore consuming less energy, to power a larger pump impeller. One such Italian pump typically consumes 550 watts to pump the equivalent of a 750 watt pump - a savings of about 36%.

Pool pumps typically are "self priming": they may be positioned above the mean water level of the pool yet still start up and function after a timed rest period. Pumps that do not "self prime" are termed "flooded suction" and must be gravity fed by the pool by being located below the mean level of the pool water.

Most pool pumps available today incorporate a small filter basket termed a "hair and lint strainer" or "lint pot" as the last effort to avoid leaf or hair contamination reaching the close-tolerance impeller section of the pump. Without these measures, the pump would need continual maintenance.

Filter Unit
A pressure-fed filter is typically placed in line immediately after the water pump. The filter typically contains a media such as graded sand (called '14/24 Filter Media' in the UK system of grading the size of sand by sifting through a fine brass-wire mesh of 14 to the inch to 24 to the inch). A pressure fed sand filter is termed a 'High Rate' sand filter, and will generally filter turbid water down to 10 micrometers in size. The rapid sand type filters are periodically 'back washed' as contaminants reduce water flow and increase back pressure. Indicated by a pressure gage on the pressure side of the filter reaching into the 'red line' area, the pool owner is alerted to the need to 'backwash' the unit. The sand in the filter will typically last five to seven years before all the "rough edges" are worn off and the more tightly packed sand no longer works as intended. Introduced in the early 1900s was another type of sand filter; the 'Rapid Sand' filter, whereby water was pumped into the top of a large volume tank (3' 0" or more cube) containing filter grade sand, and returning to the pool through a pipe at the bottom of the tank. As there is no pressure inside this tank, they were also known as 'gravity filters'. These type of filters are not greatly effective, and are no longer common in home swimming pools, being replaced by the pressure-fed type filter.

Other filter media
Other filters use Diatomaceous earth to help filter out contaminants. Commonly referred to as 'D.E.' filters, they exhibit superior filtration capabilities. Often a D.E. filter will trap water-borne contaminants as small as 1 micrometer in size. D.E. filters are banned in some states, as they must be emptied out periodically and the contaminated media flushed down the sewer, causing a problem in some districts' sewage systems. (Refer to the diatomaceous earth article for D.E. safety considerations.) Other filter media that have been introduced to the residential swimming pool market since 1970 include sand particles and paper type cartridge filters of 50 to 150 square feet filter area arranged in a tightly packed 12" diameter x 24" long (300mm x 600mm) accordion-like circular cartridge. These units can be 'daisy-chained' together to collectively filter almost any size home pool. The cartridges are typically cleaned by removal from the filter body and hosing-off down a sewer connection. They are popular where backwashed water from a sand filter is not allowed to be discharged into the aquifer.

Skimmers
Water is typically drawn from the pool via a rectangular aperture in the wall connected through to a device fitted into one (or more) wall/s of the pool. The internals of the skimmer are accessed from the pool deck through a circular or rectangle lid, about 1' 0" in diameter. On lifting the lid (if the pool is operational) you will see water being drawn from the pool, over a floating weir (operating from a vertical position to 90 degrees angle away from the pool, in order to stop leaves and debris being back-flooded into the pool by wave action), and down into a removable "skimmer basket", the purpose of which is to entrap leaves and other floating debris. The aperture visible from the pool side is typically 1' 0" wide by 6" high, which intersects the water midway though the center of the aperture. Skimmer with apertures wider than this are termed "wide angle" skimmers and may be as much as 2' 0" wide (600 mm). Skimmers form a vital link in the pool recirculation system, as they act as an initial catchment for leaves etc which could be sucked though the suction side of the system, creating the possibility of either a blockage underground between the pool and the pool shed (not easly located and fixed) or be sucked into the pool pump, thus blocking it.

Scum gutters
Arguably an unfortunate-sounding name, the descriptive "scum gutter"-equipped pool typically has the entire inner perimeter of the pool stepped down to a 12" wide ledge (300mm) at the required mean pool water level, the ledge incorporating a slotted grill covered longitudinal 4" wide x 4" deep (100 mm x 100 mm) drainage system which conveys overflowing pool water to the filtration plant (usually) via an underground catchment and top-up tank. Often the remaining pool wall is 4" higher than the Scum Gutter eliminating the possibility that pool water can overflow onto the adjacent pool surround. Other designs may not have this feature, relying substantially on a wider drainage system - 1' 0" or more (300mm) wide so as to trap any overflowing water, as typically the pool surround is at the same level as the pool water. Pools equipped with these skimming systems are typically an idea based on an Architect's ideals of design, rather than functionality. These pools are not a practical design for an active family, due to the need to continually top the pool water up if the drain's design goal is defeated by robust activity by the pool users (notably, children). An extension of the "scum gutter" pool is to build the pool "out of ground" - say 1' 0" (300 mm) and tile the pool top and exterior wall, placing the drainage system completely around the perimeter of the pool at the base of the exterior wall. In this way, the pool is visually transformed into a total "vanishing edge" pool. This design has been used to great effect in prize winning contemporary home design, notably in Southern California and the surrounding desert states.

Pool water returns
The final link in the pool recirculation system: skimmer-pump-filter-returns are the water returns. Typically these are referred to as "eyeballs" as they incorporate a swiveling nozzle that can be locked down to point in the desired direction and are reminiscent of a swiveling human eyeball. The directional adjustment is usually a 360 degree radius circle of 45 degrees away from the pool wall. Most home pools would incorporate at least two such "eyeballs". One recent development in skimmers was the 1970s "Aquagenie(TM)" which differers considerably operationally from conventional skimmers—most of which are quite similar in operation, if not appearance—by both drawing the pool water and returning it to the same location through a submerged slot which diverts the water downwards and in a wide fan shape. The concept incorporates a reservoir system to contain saturated trichor tablets which the resulting high strength chlorinated water dribbles back into the recirculation system, so it doubles up as a chlorine feeder as well as a normal skimmer. Arguably an "improvement" in skimmer design, patents on the device expired in 2003 and the system is now available from several US manufacturers.

Other equipment
Other equipment which may be optioned in the recirculation system include heat pumps/gas heaters, saline chlorination units, ionoisers, Tri-Chlor Feeders, diversions to solar panels, etc. are in most cases required to be placed after the filtration plant, and are the last item before the water is returned to the pool.

Outdoor structure
Most swimming pool installations incorporate an outdoor structure designed to house the pool filtration equipment as a protective measure against premature deterioration from sunlight and rain. Typically, these structures range in size from a simple flip-lid three-sided sound-insulated box set against a convenient house wall, the lid being constructed on a 15 to 20 degree slope and the interior large enough to hold the filter plant, pump, and whatever chlorination system has been included—up to a full-size Pool House (AKA "Pool Shed") with separate pool equipment area, bathroom, shower, changing areas, and in some cases even a rumpus-room type entertainment area. As pool-side parties are common amongst pool owning families, the Pool House forms the focal point for adult attendees, while the pool itself remains the realm of the children. (Vigilance for the safety of young children swimmers must be observed at all times, and a designated adult should be present at the poolside in a supervisory capacity)

Consecutive dilution
A pool filtration system as described (above) is termed a "consecutive dilution" system, as a constant and consecutive stream of fresh, chlorinated, and filtered water is being continually returned to the pool as part of a process that could ultimately result in a pool with 100% newly introduced fresh water over a period of time. Of course this goal is never achieved, as there is also a constant stream of new contaminants entering the pool as subsequent sections of this page will indicate.

Potential of contamination in bodies of water used for swimming & bathing
Transmission of disease from unfiltered/untreated swimming pool and spa water which may have become contaminated by germs from infected swimmers, incoming water from an unsanitary source, airborne contamination from rainfall, and droppings from birds, is possible. Contaminated water can lead to a variety of diseases including diarrhea and skin, ear, and upper respiratory infections, particularly if the swimmer's head is submerged or the water swallowed. Check the National Library of Medicine and search the database for "contamination of swimming pool water" for cases of contamination recorded http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?CMD=search&DB=pubmed.

Illness or infections associated with swimming pools, spas, and other recreational-water environments has been linked to fecal contamination of the water due to feces released by bathers or even contaminated source water. Many of the outbreaks related to public swimming pools have occurred because disinfection was poorly maintained - or not introduced at all. The solution for private swimming pools owners is to maintain the filtration and sterilization system in satisfactory working order.

The majority of reported swimming pool-related outbreaks have been caused by viruses; recently, however, reported outbreaks have been more frequently associated with bacteria and protozoa.

Non-fecal human shedding (e.g., from mucus, saliva, skin) in the swimming pool, spa or similar recreational-water environments is a source of potential non-enteric pathogenic organisms. Mucus, saliva and skin of infected users can directly contaminate pool or spa waters and the surfaces of objects or materials at a facility with sufficient numbers of primary pathogens (notably viruses or fungi), which can consequently lead to infections in other swimmers who come in contact with the contaminated water or surfaces.

Opportunistic pathogens (notably bacteria) can be shed from users and transmitted via contaminated water in pools or spas. In addition, certain free-living aquatic bacteria and amoebae can grow in pool or spa water, in pool or spa components or facilities (including heating, ventilation and air conditioning [HVAC] systems) or on other wet surfaces within the facility to a point at which some of the opportunistic pathogens may cause a variety of respiratory, dermal or central nervous system infections or diseases. Diarrheal illness subjects are likely to contaminate the water, but may not be common in pools due to the illness affecting their wellbeing and desire to go swimming. On the other hand, children wearing diapers or youngsters just learning to control their bowels are more likely to have fecal accidents and, if they are also ill with diarrhea, may contaminate the pool. For this reason, it is advised that young children wearing diapers should not be allowed in a pool with other swimmers, as if others accidentally swallow this fecally contaminated water, they can become ill. Germs such as Cryptosporidium (crypto) may come in the municipal piped water supply (mainly in countries with bad sanitation conditions), and are not easily killed by disinfectants in the pool. The advent of molecular techniques has conducted to characterize different species and genotypes of Cryptosporidium infecting humans. The vast majority of human cases of cryptosporidiosis in the world are caused by both species, Cryptosporidium hominis and Cryptosporidium parvum. However other species including Cryptosporidium felis can infect humans too. To date this (felis) emerging protozoan disease is present in humans around the world, except in Australia and Oceania.(Source: Service de Parasitologie et Mycologie medicales, Faculte de Medecine et Centre hospitalier universitaire d'Amiens, Universite de Picardie Jules Vemrne, 80054 Amiens, France. raccurt.christian@chu-amiens.Fr)

Potential diseases in poorly maintained public swimming pools

 * See more details in waterborne diseases

Although extremely rare in Western society, the most frequently reported illnesses in countries that do not enforce a strict code of health compliance in public pools, are caused by germs such as Cryptosporidium (crypto), Giardia, E. coli O157:H7 (E. coli), and Shigella. Some of these outbreaks may affect thousands of swimmers, although it is not common to see such pubreaks in the daily press or TV.

Crypto is the major germ that causes outbreaks in public swimming pools and public spas, where its extreme chlorine resistance and small size make it a difficult problem for even the best equipped and well-maintained pools. Major outbreaks associated with Giardia have reportedly occurred in systems that do not use filtration/recirculation systems or have an undetected defect in the filtration system.

Some rural or back-country pools may use a "continuous replacement" system instead of proper filtration, whereby a new source of water is introduced at one end of the pool, and allowed to drain away at the other. An example would be a public access pool using a rural creek or spring which has been dammed to form a "swimming hole", and thus may be included in the description "artificial pool". A swimming pool filtration system which utilizes pump-fed sand (or other) filter media in a closed loop recirculation system is termed a "continuous dilution" system, as freshy filtered and chlorinated water is continually fed into the pool, thus diluting the turbidity and bacteria levels.

E. coli and Shigella are relatively sensitive to chlorine or bromine so most outbreaks have occurred in locations where no disinfectants are added, such as hot pools or spas that are filled with underground thermal waters. In certain countries, fatal primary amoebic meningoencephalitis (caused by Naegleria fowleri) has occurred following swimming in warm dirty thermal water, where the bather has immersed his/her head under the water. Other non enteric pathogens that may be found in swimmming pools and hot tubs are Legionella spp., Pseudomonas aeruginosa, Mycobacterium spp., Staphylococcus aureus, Leptospira interrogans, Molluscipoxvirus, human papilloma virus, Acanthamoeba spp., Trichophyton spp., and Epidmermophyton floccosum, that usually produce dermic or respiratory infections.

While not typically spread in pools from one person to another, several other illnesses can also develop with poor sanitation or improper personal hygiene. The most common infection is Otitis externa - commonly known as swimmer's ear, an infection of the ear canal. Another called Pseudomonas aeruginosa (mentioned above) requires special mention and can be spread from human to human in swimming pool water. However, it is generally not a problem for most people unless they are also suffering from immuno-deficiencies such as hepatitis or Human immunodeficiency virus or HIV infection. Pregnant women are also at high risk. Others may experience a rash or other skin irritation. If suspected, at risk individuals who have been exposed should be tested and local health officials should be contacted.

Most modern public swimming pools now use a flocculate, generally Polyaluminium Chloride (PAC), which, when added to the pool circulation, before filter, provides another defense against virulent germs, such as Cryptosporidium. It lines the top of the filter bed, capturing tiny bacteria and allowing them to be removed as part of backwashing (normal cleaning procedure for pool filters). This is the only way to properly manage the risk of contamination from such germs, and is now fairly standard in the leisure industry.

Prevention of diseases in swimming pools and spas
Disease prevention should be a part of every water quality management program for pool operators, just like the prevention of drowning, injuries, and sunburn. People are less likely to be exposed to polluted water at swimming pools and spas that are monitored regularly and audited for health hazards. The pool water has to be continuously disinfected by disinfectants so that the concentrations set by standards are maintained throughout the pool water, and also the pH, the clarity and the total alkalinity of the water has to be maintained in accordance with the requirements set by standards.

The education of parents of small children and other people with regard to good hygienic behavior at swimming pools is also important for improving health safety at swimming pools and spas. People should also be cautioned about swimming in pools if they are suffering from gastroenteritis or other illnesses where viral pathogens might be transmitted from swimmer to swimmer via pool water.

Since most swimmers are exposed to pathogens by swallowing the water, people will be less likely to get sick if they swim without submerging their head.

Strong oxidizing agents are often used, especially simple chlorine compounds such as sodium hypochlorite. Other disinfectants include bromine compounds and ozone. Chlorine, bromine, and ozone can all be generated on site by passing an electrical current through either the pool water itself, in the case of chlorine or bromine, or through oxygen or air, in the case of ozone. Chlorine may be supplied as a hypochlorite solution (bleach), powdered calcium hypochlorite ("cal hypo"), chlorinated cyanurate compounds ("stabilized" chlorine such as dichlor or trichlor), or by dissolving chlorine gas directly in water. Maintaining a safe concentration of disinfectant is critically important in assuring the safety and health of swimming pool users. When any of these pool chemicals are used, it is very important to keep the pH of the pool in the range 7.2 to 7.6; higher pH drastically reduces the sanitizing power of the chlorine due to reduced oxidation-reduction potential (ORP), while lower pH causes bather discomfort, especially to the eyes. Chlorine reacting with urea in urine from bathers can create nitrogen trichloride, which has a teargas-type effect.

Where the water is sanitized by means of oxidizers, some suppliers of electronic monitoring equipment recommend that the efficacy of the oxidizer be measured by the oxidation-reduction potential of the water, a factor measured in millivolts, where the minimum acceptable ORP level in public pools is 650 millivolts. This is supposed to ensure a 1-second kill rate for microorganisms introduced into the water. Unfortunately, a commonly used non-chlorine supplemental oxidizer, potassium monopersulfate, can produce measured 650 mV levels even in the absence of all sanitizing residuals. Cyanurated ("stabilized") chlorinators can give falsely high chlorine readings when tested with OTO (ortho-tolidene, a yellow indicator dye used in inexpensive test kits), since the chlorine indicated by the dye is mostly in a combined form instead of free, and does not contribute to ORP. ORP test cells are available as hand-held instruments, and as probes for mounting permanently in the pool circulation plumbing to control automatic chlorine feeders.

Test kits to make basic measurements of free chlorine and pH from a sample of pool water, which are the most important items to control in a swimming pool, are packaged with small dropper bottles of reagents. These reagents are typically OTO for chlorine and phenol red for pH. OTO has been phased out in most countries due to a connection with the production of cancer cells in test rats. More commonly DPD tablets replaced OTO since 1980. The kits include vials for mixing a water sample with the test reagents, and color charts for reading the indicated levels. These kits are termed "Comparator" kits as the test is "compared" to a known color value. Besides chlorine and pH, which should be checked frequently, more sophisticated reagent kits provide tests for acid demand and base demand, total alkalinity (TA), calcium hardness, and cyanurate ("stabilizer") concentration. These additional tests tend to vary only over weeks or months in a well-maintained pool, and thus need not be checked as frequently as chlorine and pH.

In the 1970s the Taylor Watergram introduced the relationship between the compounds and chemicals desired to be present in pool water. When the requirements of relationship were met, the pool was considered to be "balanced". A residential pool that is in proper "balance" would have a pH of 7.6, Calcium Hardness of 200 ppm (parts per million), Sodium Bicarbonate level of 120 ppm—and a residual chlorine level of 1.0 to 2.0 ppm.

Residential swimming pools generally rely on "breakpoint chlorination" i.e. the amount of residual chlorine present in the water is sufficient to combat the daily introduction of nitrogenous based matter and yet leave a positive residual. This is generally arrived at by a process of experimentation on the part of the pool owner.



Pool sanitation, which necessarily involves toxic or mechanical means of killing microbes, can sometimes unintentionally irritate the swimmers, especially if poorly maintained, especially a too high level of chlorine and/or too low pH. Non-chlorine sanitizing chemicals and devices are promoted as being less harsh, but any sanitizer is harsh if overused. Water circulating through a pipe can be sterilized with UV light instead of chemicals, but some level of chemical sanitizer is still needed, because only a small portion of the pool water passes through the circulation system at any given time, and the circulation system typically only runs for a few hours each day. UV sterilization also does not inhibit algae from growing on pool surfaces, and it does not break down dissolved nitrogenous nutrients that feed algae growth, so some type of oxidizing sanitizer is still needed to check these trends, although it need not be dosed during bathing hours for this purpose.

"Chlorine smell" is misunderstood, as chlorine is a colorless(slightly yellowish), odorless gas. What can occur is that insufficient chlorine is called upon to disinfect a heavily contaminated pool. In the incomplete reaction that follows, a by-product called "chloromine" is produced, and chloromines are responsible for the smell. The way to remove these chloromines is to "super-chlorinate" the pool with a dose of 10ppm of Cal-Hypo. Regular superchlorination (every two weeks in summer) will eliminate these unpleasant odors in the pool.

Generally, a well managed pool will have no smell or taste, be scrupulously clean, and have crystal clear water. Most people would not want to swim in a pool that appears dirty even if germs were under control. A pool pump circulates water through a strainer and filter to remove dirt and other suspended particles. The plumbing circuit may also include a gas or electric heater, solar panels, and chemical injector.

The proper management of a backyard swimming pool can be a difficult and time-consuming task. The chemical balance of the water has to be monitored carefully to make sure that it does not become fouled with algae or bacteria. Either of these will make the water smell and look unpleasant and can be a serious health hazard. The water must also be kept clear of debris such as fallen leaves and sticks, as these encourage fouling and become very slippery and dangerous as they start to decompose. Most people keep their pool either covered over or drained entirely during the months of the year in which it is not in use, as this is the easiest way to keep it sanitary (draining however can be a serious safety hazard with deeper pools and re-filling can be fairly expensive in areas where water is scarce). Public and competitive swimming pools are therefore often, especially in colder climates, indoor pools&mdash;covered with a roof and heated&mdash;to enable their use all year round.

Chlorine generators (salt systems)
Chlorine may be generated on site, such as in saltwater pools. A New Zealand device the Aquatech IG450 home pool saline chlorinator was introduced to the residential swimming pool industry in 1973 when the first commercially manufactured units for home use were shown at the 1973 Chicago Trade Fair. In the following years, many US, Australian and South African companies duplicated the device, as the process of creating chlorine from saline water - a natural process that occurs in nature when lightning strikes the ocean - was not Patentable. This process generates chlorine by low-voltage electrolysis of dissolved salt (NaCl) using an electrode incorporated in the pool plumbing, eliminating the requirement of manually dosing the pool daily with powder chlorine. Chlorine generators avoid the need for constant handling of dangerous sanitizing chemicals, and can generate sanitizing power at a lower cost than equivalent chemicals, but they have a significant up-front cost for the apparatus and initial salting of the pool. Annual rainfall contributes to dilution of the pool water, which will require regular "topping up" with several 50Lb (20Kg) bags of salt for the average size pool.

Another issue is the production of equal amounts of Sodium Chloride and Sodium Hydroxide (ph = 14, or Base) which causes the pool water pH to rise to levels that render the production of useful chlorine HOCl to levels as low as 15% while the balance of the chlorine produced converts to OCL. OCl still maintains some bacteriacidal properties, but is only effective in concentration of 25,000ppm, so in effect is useless. This dramatic swap occurs in water where the pH is exceeds 8.0. This renders the saline system less effective unless a close watch is kept on pH levels. Some saline units in production (2007) have incorporated an acid demand test, and the pH is maintained at the correct level by periodic shots of acid into the system. The downside of these units is the need to store large quantities of Hydrochloric Acid on the pool site which must be secured for safety if young children are present.

Early salt chlorinators required 2.0 ppm dilution, and this content gave the pool water a slightly salty, brackish taste, but not as salty as seawater which is around 20.0 ppm. Modern units use far less salinity - around 0.2 ppm to 0.4 ppm and the salt cannot be detected by taste. Pool water that splashes and evaporates, such as on a pool deck, leaves a salt residue. Being closer to isotonic salinity (0.9%) than fresh water, saltwater pools have an easier feel on the eyes, and a touch typically characterized as "silky", not unlike bath salts.

Ionization systems
Ionization systems using copper and silver, destroying bacteria and algae, are optional replacements for chlorine systems. In this method low amounts of chlorine are necessary to combat algae. The pool water runs through the ionization cells and is disinfected using a low electrical current. A control unit can decide how much copper and silver to release into the pool, reducing manual maintenance. The cost for such a system is no higher than that of a saltwater chlorine generator, which can be more expensive than the standard chlorine disinfection systems. This method of pool water sterilization was under a recall notice by the APVMA (2004) in Australia, pending an appeal from the local manufacturers of Ioniser units. As a result of a successful Administrative Appeals Tribunal challenge, both the Aquabrite System, [www.aquamatics.com.au] and the PoolFresh System, [www.monarchpoolsystems.com/] were granted permits by the APVMA.

Ozone generators
Ozone use is becoming more prolific as a booster device that will reduce the requirement for Chlorine to be used in home swimming pools. Highly bacteriostatic, pools equipped with ozone units report a 75% reduction in chlorine demand. Ozone is short-lived, generally completely depleted within five minutes of introduction into the pool, but is highly effective in killing all unwanted pathogens in the water which passes through the unit. There are two basic types of ozone generators: the flourescent, and catalyctic cracker. The latter device is more effective, but the devices are more costly. Both units rely on a vortex suction device placed in the pool water return line to draw air through the device, thus resulting in air bubbles being evident where the water is returned to the pool.

The above design, although common, would be considered to be poorly engineered. From the ozone injector the water should enter a contact tank before return to the pool. Proper system design is straightforward but rather complex in that the hydrology of the entire pool and pumping system comes into play. There is no such thing as "standard" or "off the shelf" systems, that would more likely be purely marketing hype or ignorance.

Biguanides
Other more recent sanitizers have also been introduced as of the early 1990s and are referenced as Biguanides. Biguanides were originally developed for the medical industry and utilize the polymer PHMB (polyhexamethylene biguanide). Biguanides are generally less harsh and more stable in the pool water, but are also more expensive and require the periodic addition of extra strength hydrogen peroxide and can react very harshly with chlorine or other sanitizers.