FAQ’s on Ozone in Pools and Spas
( AQUAZONE OZONE GENERATORS)
Q1. Why ozonise / ozonate my pool or spa?
- 1. a. Generally pool owners who are concerned about harmful effects of chlorine will be interested in converting from chlorine or chemicals systems and/or salt chlorinators.
In particular heated pools or spas with chlorine disinfectant systems can be harmful as the skin pores open up with the warm water and chlorine can be ingested in to the
Health authorities in first world countries insist on a residual level of 2.5 to 3 ppm (
parts per million) chlorine in public pools for effective sanitation. At these levels the
chlorine smell is very evident and uncomfortable and unhealthy to many…even if the
water is sanitised! By including ozone in the circulation system it is possible to bring
the levels of chlorine down to a much safer 1 ppm and the water is sanitised and safe
Competitive or regular swimmers will often refuse to swim in a chlorinated pool and
Olympic and Municipal pools are generally ozonated for this reason.
- Dependingupon the cost of electricity or chemicals and the amount of
circulation/pumping time, ozonated systems will be cost effective once the capital
costs are amortised after 2 or 3 years.
Q2. What size unit do I need for my pool.
- 2. Sizing depends upon many factors
- Runningtime and output of the circulation pump. Generally speaking if the pump
output is 1000 litres per hour 1 gram an hour of ozone will be sufficient to
sanitise the passing stream.
- Temperatureof water. ( the colder the better).
- Amountof bathers in the pool.
- Capabilityor effectiveness of the ozone gas induction and mixing system. (A 1000
mg/hr ozone generator with an efficient mixing system could be as effective as a 5000
mg/hr generator and an inefficient mixing system). Ozone, being a gas, must be
effectively introduced in to the water flow using a venturi and then thoroughly mixed
with the water before entering the pool.
There should be sufficient contact time for the ozone to mix with the water and to
react before entering the pool. ( The longer the better).
- Actualoutput of the ozone generator.
Systems using atmospheric air as the feedgas will provide lower outputs at high
The airflow determined by the venturi must match the ozone generator. ( Aquazone
systems generally require between 3 and 5 litres of air per minute).
The venturi suction is affected by the cleanliness of the filter or back pressure caused
by a connected self cleaning vacuum system.
- Amountof chemicals used by the owner.
If the pump is not running 24 hours per day, chemicals will be required to provide a
residual control whilst the ozone is not being introduced.
Depending upon the shape of the pool it may be necessary to introduce chemicals in
various corners where circulation of the water does not occur.
As a general rule 1000 mg/hr in a reasonably dry atmosphere with an efficient injection and
mixing system, running for 8 hours per day, at normal temperatures, with 15% of normal use
of chemicals, and 2 or 3 bathers per day should be adequate for a 50000 litre pool.
Therefore a 100000 litre pool in similair circumstances will require 2 grams of ozone per hour.
Q.3. How much maintenance is required.
A.3. The ozone generator must be kept clean and in a cool dry place. Gas and water lines
should be checked regularly for leaks and blockages. Non return valves and static mixers ( if
fitted) should be checked regularly.
Q.4. What is ozone?
A.4. Ozone is a highly reactive form of oxygen. It is a gas and is slightly soluble in water. It
is the fresh smell during and after thunderstorms. An ozone smell can sometimes also be
detected around office machines and laser printers. In fact, ozone in air can be readily
detected by smell at concentrations as low as 0.03 ppm (parts per million).
Because a single oxygen atom is very unstable, it travels around in pairs, which is written
scientifically as O2. Ozone is made up of three oxygen atoms together, written as O3. It is
called tri-atomic oxygen, activated. It very effectively kills small organisms like bacteria and
virus. The amount of ozone that is deadly to bacteria and germs is safe and non-toxic to
Q.5. Is ozone new?
A.5. Ozone has been around as long as oxygen, sunshine and lightning. It was discovered
and isolated in 1840 by C. F. Schonbein who noticed a unique odour during electrical
sparking and electrolysis experiments. He realised that the odour was the same one he
observed after a lightning flash. He named the substance ozone from the Greek word ozein,
which means, “to smell”.
In 1886 de Meritens of France conducted the first experiments using this unique gas as a
disinfectant. He proved that even minute amounts of ozonised air would sterilize polluted
water. A few years later in 1891, the German scientist Frolich reported the bactericidal
properties of ozone from pilot plant tests conducted at a drinking water treatment plant in
Martinkenfeld, Germany. In 1893, the first drinking water treatment plant to employ ozone was
built in Oudshoorn in the Netherlands. In 1906, the first large-scale water treatment facility
built specifically to use ozone as a disinfectant was completed. By 1977, there were 1039
ozone drinking water treatment plants in Europe. Today there are more than 2000 water
treatment plants worldwide using ozone.
Ozone has been used in swimming pools and spas in France, Germany, Netherlands, and
other European countries since the early 1950’s and in the United States since about 1975.
Q.6. How does ozone work?
A.6. Ozone is a powerful oxidiser. In fact ozone is up to 50 times more powerful at killing
bacteria and viruses than traditional pool and spa chemicals and up to 3000 times faster.
Ozone is stronger than chlorine, bromine, hydrogen peroxide and non-chlorine shock
treatment chemicals. However, because it is so reactive, ozone only lasts in the water for a
Ozone is faster than chlorine at killing bacteria because chlorine needs to diffuse through the
cell wall and disrupt the bacteria’s metabolism. Ozone, however, rips open the cell wall from
the outside, causing the cell’s contents to fall apart. This process is called cell lysing. With
ozone, after destruction of the cell, all that is left is carbon dioxide, cell debris and water.
As the ozone oxidizes material, it gets used up. Once it has done its job of oxidation, ozone
reverts back to oxygen (O2). This additional oxygen in the water makes it taste good, smell
good and gives it a sparkle. There are no toxic or hazardous by-products.
Q.7. What will ozone destroy?
A.7. Ozone kills bacteria, viruses, spores, mould, mildew, fungi, amoebae and cysts. The
amount of ozone, the concentration of ozone, the contact time of ozone with the organism,
and other sanitizers and oxidizers being used, all play a role in the destruction of
microbiological contaminants. It will not usually eliminate algae at the concentration and
contact times used in swimming pools and spas in the U.S. An additional sanitizer must be
added to the water to kill algae and provide protection during the time the ozone generator is
Q.8. Is Ozone an Oxidizer?
A.8. The easy answer is Yes. “Oxidizer” as used by the pool spa industry used to mean
destroying everything in the water by adding a mega dose of chlorine. Then, the industry
started using the term to mean using a “non-chlorine” shock treatment chemical to rid the
water of ammonia, perspiration, and other organic matter including swimmer waste.
According to the EPA (Environmental Protection Agency), there are more than 700 different
organic products and swimmer wastes that can be in the water. Ozone can oxidize most of
them very quickly. Ozone will also oxidize metals such as iron and manganese, as well as the
bonds of many colour-producing contaminants like decaying leaves and grass. Once the bond
is broken, the colour disappears.
Q.9.. Can I stop using Chlorine (or Bromine) when I ozonise my pool?
A.9. You will certainly cut down on the amount of chlorine or bromine that you are using, but
you should not eliminate chlorine or bromine entirely. The reduction in chemical use will vary
from pool to pool, but amounts of up to 90% are possible. Ozone provides better water quality
and oxidizes many contaminants that chlorine or bromine cannot. Ozone only lasts in pool
water for a short period of time (between 3 and 18 minutes). It is injected into the water when
the pump is running. Ozone will kill algae at the point of injection, not algae that are growing
on the pool walls.
To provide lasting protection during times when ozone is not being injected, to control algae
and to oxidize ammonia and swimmer waste, you must maintain a small residual of chlorine
or bromine (0.5 to 1.0 ppm of chlorine or 1.0 to 2.0 ppm of bromine) in the water. The longer
the ozone system operates, the less chlorine or bromine you will have to use to maintain
Q.10. Does Ozone Have an Odour?
A.10. Ozone has a distinctive odour. It is the fresh smell during and after thunderstorms. It
can also be detected around office copy machines and laser printers. In fact, ozone in air can
be readily detected by smell at concentration as low as 0.03 ppm (parts per million).
Q.11. How is Ozone Made?
A.11. Ozone can be made in two ways. The first way is called corona discharge or CD. An
example of this first way is when lightning travels through our atmosphere close to earth. Our
atmosphere near earth is about 20% oxygen (O2) and about 79% nitrogen (N2). The energy
of the lightning splits an oxygen molecule into two oxygen atoms (O). This oxygen atom is
very reactive and does not like to travel alone. So it attaches itself to another oxygen
molecule making ozone (O3).
Corona discharge (CD) ozone generators produce large amounts of ozone compared to the
other ways. CD ozone generators produce ozone by passing ambient air (or preferably dried
air or oxygen) over a dialectic strip which has electrodes on either side of it, and when a high
voltage and high frequency is applied. Some of the oxygen splits apart and quickly
recombines with another oxygen molecule, thus producing ozone. The method produces
concentrations of 1.0 to 3.5% ozone.
Ozone is made a second way by exposing oxygen molecules to a specific ultra-violet (UV)
light. A special wavelength (185 nanometers or nm) is required to make ozone. Most
fluorescent light tubes have only a small amount of the 185nm light. Therefore, special UV
light tubes that emit larger amounts of 185 nm light are needed to make ozone. The sun also
emits this 185nm UV wavelength. UV rays in this range cause skin cancer and other skin
disorders. Fortunately, there is a layer of oxygen and ozone between 9 and 18 miles up in
our atmosphere. This layer is called the ozone layer. As the rays of the sun at the right
wavelength strike the oxygen molecules, they split into oxygen atoms (O) and reform with
another oxygen molecule (O2) to form ozone (O3). The ozone layer protects people by
absorbing the skin cancer-producing rays of the sun. Ozone produced by this method
produces much lower concentrations of ozone than CD generators. The amounts of ozone
produced by this method are typically 0.001 to 0.1% ozone.
Both of these methods require air or oxygen to travel into and out of a chamber so that some
amount of oxygen is converted into ozone. One additional consideration is the amount of time
the air or oxygen is in the ozone-producing chamber. If the air is in residence for a short
amount of time, less ozone is produced. If the ozone stays in the ozone chamber too long,
heat or other UV light rays will destroy the ozone. So the airflow, the amount of time, the
water and air temperature, and the level of moisture in the air are all critical to producing
Q.12. How does ozone get into the water?
A.12. Ozone is a gas and it is only slightly soluble in water. It must be thoroughly dissolved
in water so that the chemical reactions with contaminants can take place. There are three
methods of getting ozone into the water – by injector, static mixer or sparger.
The most common way in swimming pools is with an injector, which is a test tube less than a
foot in length with each end the same size as the pool plumbing line. A section of pool
plumbing is removed, and an injector is installed. The injector’s diameter is smaller in the
middle, similar to squeezing or pinching a hose. The water travelling into the injector begins to
move faster, like when you put your finger over the end of a hose to make it spray further. In
the middle of the injector there is a small hole. As water is pumped through the plumbing and
past the hole, a vacuum is created. The amount of vacuum is dependent on the amount of
water flow through the injector – more water equals more vacuum. If a small flexible hose or
tube is attached to this small hole, a liquid or gas can be drawn into the injector and mixed
into the water.
The goal is to make the smallest bubbles possible and to keep the bubbles in contact with the
water for as long as possible. The bubble/ water mixture goes into a contact chamber and
while it is there the ozone passes through the gas/ water interface, into solution. The chamber
is usually built as a tall structure so that the gas rises, and, having been effectively scrubbed
passes out of a valve at the top of the chamber. The off gas should contain negligible quantities of ozone. The ozone that does not get dissolved will kill or oxidise anything in the
Q.13. Will the temperature or humidity of the air or water affect ozone?
A.13. The temperature and humidity of the air and the chamber where ozone is made is very
important in maximising ozone output. The cooler and dryer the air, the greater the ozone
Q.14. Is ozone safe?
A.14. The ozone generator should he wired to come on only when the pool circulation and
filtration pump is on. A properly installed ozone system using a Contact Chamber will dissolve
all of the ozone into the water and not allow any ozone to escape to the atmosphere. The
HSE have established a limit for exposure to ozone of 0.2 ppm of air for a 15-minute period.
Ozone can be detected by smell at levels 10 times smaller than this.
Q.15. How long will ozone last in my pool?
A.15. Because it is so reactive, ozone only lasts in solution for a few minutes. This is the
reason that you cannot buy a container of ozone. Ozone must be made on site. Depending on
the amount of oxidisable material in your water, ozone will only last from 3 to 18 minutes. It is
therefore typically necessary to add a minimal amount of chlorine or bromine to maintain a
residual amount in the pool. If you use chlorine, keep the level between 0.5 and 1.0 ppm. If
you use bromine, keep the level between 1.0 and 2.0 ppm.
Q.16. Is ozone safe for my pool equipment?
A.16. Ozone gas can corrode metal if there is moisture in the air that is feeding into the
generator. This is why Ozone Industries Limited always supplies an Air Dryer to remove
moisture. The critical areas where ozone gas may make contact are made from special
ozone-resistant materials. Once dissolved, ozone has a near neutral pH. Therefore, it will
have no effect on water chemistry.
Caution should be used when ozone is near incompatible materials. Ozone gas is compatible
with some plastics, stainless steel, and Teflon. Other plastics may be degraded by ozone gas.
However, this does not mean that you must change all your plumbing to use ozone in your
pool. Once ozone is dissolved in the water it is not a threat to usual materials of construction.
Ozone dissolved in the water will not be a problem. Ozone Industries Limited can advise on
suitable materials in the critical areas. If an ozone purification system is installed properly with
a contact chamber, it will not damage a pool cover.
Q.17. Is ozone safe for swimmers?
A.17. Ozone dissolved in the water is pH neutral so the pH will not harm equipment or
people. The amount of ozone added to the water is enough to kill bacteria, virus, cysts, mould
and spores, but is safe and non-toxic to humans and pets – just like small amounts of other
disinfectants such as chlorine or bromine. Ozone in air can he readily detected by smell at
concentrations as low as 0.03 parts per million (ppm). When properly installed and plumbed
all of the ozone generated will be dissolved in the water or used up oxidizing impurities in your
Q.18. Does ozone affect water balance?
A.18 Ozone has a neutral pH (about 7.0) so it does not affect pH. Ozone has no calcium, no
alkalinity, and no dissolved solids. Therefore, ozone does not affect water balance. It does
remove trace amounts of metals such as iron or copper by oxidising them to their highest
oxidation state. They will then precipitate out of the water and be trapped by your filter.
Q.19. Can I run my pump and filter for fewer hours?
A.19. Ozone is only injected into your water when the pump is running. The longer you run
the ozone generator (and your pump and filter), the better your water quality and the less
chlorine or bromine you will need. During the swimming season you should run your ozone
generator, pump and filter a minimum of eight hours each day longer if there are high
swimmer loads, hot or rainy days.
Q.20. Will there be a visible change to my water?
A.20. Yes! When ozone is first introduced into your pool water and during the first 72 hours,
your pool water may get cloudy. Ozone will begin to oxidise all of those particles and metals
that your present sanitizer would otherwise leave in your pool. When these particles are
oxidized, they form visible particles that are heavier than water and precipitate. Also, there will
be pieces or fragments of the cells that ozone has destroyed. So the cloudiness that you may
see is oxidized material, pieces and fragments of cells, and metal precipitates. Some of the
dirt and debris in the water is too small to be trapped by the filter. These small-sized dirt
particles have a weak electrical charge or pole. Because all the dirt particles have a negative
charge, they repel each other like two magnets. They are so small that they are not affected
by gravity and therefore won’t settle out either. Ozone neutralizes these charges, which allows
the particles to combine into large enough particles to be trapped by the filter. Once these
particles are oxidized, neutralized and filtered, the water will have a definite “clarity and
sparkle” that you may not have experienced before. In addition, after the ozone does its work,
it reverts back to oxygen. This added oxygen will make the water look, feel and even taste
Q.21. What special maintenance does ozone require?
A.21. You may discover that some of your usual pool maintenance jobs are easier or do
not need to be done as often. You may find your filter cleaning needs may vary. Please refer
to your filter manufacturer’s recommendations for determining when and how to clean or
backwash your filter. You typically find that you have to clean the “bath tub ring” or scum line
or water line on the tiles less often also. The Aquazone unit only requires an occasional
inspection to ensure the operating lights are on when the unit is making ozone, and off when
the pump is off. Because ozone will be doing most of the work, you will be adding
significantly less chlorine or bromine. And using less sanitizer, you may also have to add less
Q.22. What chemicals should not be used with ozone?
A.22. Basically, all chemicals that you use with other sanitizers like chlorine or bromine are
compatible with ozone. Of course, using ozone will reduce the amount of chlorine or bromine
that is needed. Most sanitizers (chlorine and bromine compounds) have either a high or low
pH. Therefore, when you use chlorine or bromine, you must add a pH-adjusting chemical
(acid or soda ash) to compensate. Ozone may also reduce the frequency of chemical
additions and filter runs. Do not use red hypochlorite as this contains manganese which
ozone will oxidize.
However, certain broad-spectrum polymer sanitizers whose active ingredient is
Polyhexamethylene biguanide are not compatible with ozone. Ozone will oxidize and destroy
part of the biguanide polymer, which will then form a dark precipitate that may clog filters and
stain pool walls and bottom. Ozone Industries (PTY) Ltd does not recommend using these
products. Check label for chemical content if using polymer sanitizers.
Q.23. Will I still need an algaecide?
A.23. First, understand that algae do not cause any disease. However, algae can be a
harbouring place for bacteria, and it is unsightly, slippery and a nuisance. It just looks bad.
With all of the other “oxidizable” material (such as bacteria, swimmer waste, suntan oil, etc.)
in the water, ozone probably will only get a chance to kill algae that gets near the ozone
injector. Algae growing on the walls or bottom will not be killed by ozone. This is but one of
the reasons that small amounts of chlorine or bromine must be added to the water to protect
from algae bloorns. Also, remember those ozone only stays in the water for a few minutes, at
best. When the circulation equipment and the ozone generator are off there is no residual
ozone left in the water. The pump “off time” may be 16 to 18 hours per day. Therefore, a
chlorine or bromine residual kept in the water at all times will kill, protect and control algae, as
well as destroy ammonia, swimmer waste, oils, etc.
If you are maintaining a pool properly, you will not have algae. This is true whether you are
using ozone, chlorine or another sanitizer. Most algaecides are compatible with ozone.
However, be sure to advise your pool service technician or professional pool dealer that you
have an ozone generator before selecting an algaecide.
Q.24. Will I still need to “shock” my pool?
A.24. Shocking can mean to add a megadose of chlorine (super-chlorination) or to add a
non-chlorine shock treatment chemical. The ultimate goal is to rid the water of ammonia,
nitrogen-containing compounds and swimmer waste. Ozone will not be in the water long
enough to completely oxidize these. Therefore, you must rely on a low residual of chlorine to
destroy them. If the residual chlorine does not destroy them, then you must oxidize with a
non-chlorine shock-treating compound or you must super-chlorinate. Both of these methods
will destroy ammonia, nitrogen-containing compounds, and swimmer waste; however,
chlorine has the added advantage of being able to also kill bacteria. Bromine does not destroy
ammonia and nitrogen-containing compounds and swimmer waste. You must shock with
chlorine or a non-chlorine shock if you are sanitising with bromine.
Q.25. Should I do anything special when I have a pool party?
A.25. A large number of people getting into any pool are going to use up all of the available
sanitizer, whether it’s ozone, chlorine of bromine, very quickly. Having a little extra chlorine or
bromine in the water avoids being unprotected.
You may therefore wish to super-chlorinate a day or two before the party. Add chlorinating
chemicals according to the manufacturer’s label. Although you may have been using only 0.5
to 1.0 ppm of chlorine, the accepted chlorine level for protection is 1.0 to 3.0 ppm. The
chlorine level in your water can exceed 3.0 ppm during super-chlorination, however,
swimmers and bathers should not enter the water until the chlorine level is below 3.0 ppm.
If you are using bromine, super-chlorinate as above or add a non-chlorine shock treatment
chemical per manufacturer’s instructions. Although you may have been using only 1.0 to 2.0
ppm of bromine, the accepted protection range for bromine is 2.0 to 4.0 ppm. Swimmers and
bathers should not enter the water until bromine levels are under 5.0 ppm. It may also be a
good idea to super-chlorinate after a large pool party. The extra chlorine or shock will destroy
all the swimmer waste right away.
Q.26. Will my ozoe generator help the ozone layer?
A.26. Ozone from a swimming pool ozone system will not add anything to the atmosphere or
the ozone layer. When injected into the water properly, no ozone escapes into the
atmosphere. Even if it does get into our atmosphere, it is like a drop in the ocean. Also, the
ozone would have to be transported 9 to 18 miles up. The ozone layer that you may have
heard about is a layer of mostly oxygen and ozone that is located in the lower stratosphere
between altitudes of 9 and 18 miles. This ozone results almost entirely from oxygen (O2)
splitting apart into two atoms of oxygen (O) by solar ultraviolet radiation (the sun’s UV rays)
and then combining with molecular oxygen (O2) to form ozone (O3).
Atmospheric ozone plays a critical role for the earth by absorbing the ultraviolet radiation from
the sun with a wavelength of between 240 and 320 nanometers (nm), which would otherwise
be transmitted to the Earth’s surface. This radiation is responsible for sunburn to human skin.
In addition, the incidence of skin cancer has been statistically correlated with UV light
intensities of 290 to 320 nm.
Q.27. How do I know if there is enough ozone for proper sanitation?
A.27. This can be a difficult question to answer. Experts have not been able to develop a
minimum or maximum level for ozone in swimming pool water because of the multiple
variables involved such as air temperature, water temperature, humidity and bather load.
Pool owners who have been using chlorine of bromine for a few seasons know how much
sanitizer they use in a season or year. Installing an ozone generator in these pools has
resulted in a significant reduction in the amount of chemical sanitizer used. The longer the
ozone operates each day, the greater the reduction in chemical sanitizers. Pool owners have
had reductions in sanitizer use of 50 to 90%. Your savings may vary based on pool usage
The Aquazone selected for your pool has been arrived at by field tests, best available
information from other industries like drinking water, water-cooling towers and extensive lab
testing. Ozone Services Industries Limited feels this is an appropriate and sufficient level for
proper sanitation of residential swimming pools.
Ozone is not sold on the basis of being less expensive than other sanitizers such as chlorine
and bromine are. Its value is in smoothness and sparkle to the pool water, elimination of the
dry, itchy skin that chemicals can produce burning red eyes and bleached bathing suits. Other
important advantages include reduced pool maintenance and reduced exposure to toxic
chemicals in storing, handling and swimming.