To Chlorinate Or Not To Chlorinate?

A Natural Swimming Pond

Eau de chlorine the swimmers’ perfume, or does it have to be?  Until I started teaching, I was only aware of chlorinated or salt water swimming pools, but actually there are more than two options to keeping your pool clean.


Chlorine isn’t just chlorine.  There are in fact five different types of chlorine and these can be broken down into two sub-categories.

Stabilised Chlorine:

Dichlor and trichlor are the two stabilised types of chlorine.  They are stabilised because they contain cyanuric acid, which acts as a type of sunblock and so makes them suitable for outdoor swimming pools.  The sun breaks down chlorine causing it to burn off quicker and the cyanuric acid will slow this process down.

Dichlor or sodium dichloroisucyanuate dihdrate comes in chlorine granules and the recommended dosage would be two to three parts per million.

Trichlor is an abbreviation of the chemical name trichloroisocyanuric acid and comes in the form of slow dissolving tablets of 200 gm. for most pools or 20 gm. for use in small pools and spa baths.
Neither type of stabilised chlorine is suitable for shocking or super chlorination.

Unstabilised Chlorine:

Calcium hypochlorite is more commonly seen in granules, but can also come in tablet form.  Calcium hypochlorite is the most popular of the chlorines to use in swimming pools, both at home and commercial, it can be used to shock the pool, but is also used in erosion feeders as the main way to disinfect the pool.

Sodium hypochlorite is a liquid chlorine and because of this, is usually applied to a pool through an automatic chemical feeder.  Water parks and commercial pools, which are typically large in size, are the common users of this form of chlorine.

Lithium hypochlorite comes in a granular format which dissolves very quickly in water which makes it ideal for shocking (super chlorinating) fibreglass and vinyl lined pools and pools situated in areas with high hard water and calcium levels.  Due to the fact that lithium hypochlorite has a low active strength and the high cost involved, it is only really suitable for home pool disinfectant rather than commercial.


Though chlorinated swimming pools are still the most popular, other methods of treating pools are gaining in popularity.  Saltwater swimming pools have several advantages over that of a chlorinated pool, including being kinder to your skin and hair, minimal maintenance, fewer chemicals and in the long run, lower cost of upkeep.

It might be surprising to discover, that actually a saltwater pool does use chlorine.  However, in a normal chlorinated swimming pool, the chlorine is manually added on a regular basis to dissolve in the water, whilst in a saltwater pool, a regenerative process creates the chlorine.  A saltwater pool relies on an on-site saltwater purification system to provide sanitiser to keep the water safe, healthy and free from algae.  The sanitiser does not require any handling, storage or pumping the water full of chemicals, as it is produced automatically within the water itself.  As long as the sanitiser system is the correct size for the pool in question, no other cleaning chemicals, such as chlorine, will need to be purchased.

The salt used to make a pool saltwater is sodium chloride, the same substance that is used in food preparation.  The concentration of salt is about one tenth to one twelfth of that of seawater, thus creating a mild saline solution.  A chlorine generator is added to the pool’s filtration system, which is what the water passes through as part of the cleansing cycle.  The chlorination happens here when the saline solution is subjected to electrolysis and the chloride part of the salt is converted into a sanitiser, which will then kill of any bacteria, viruses, and algae present in the water.  This sanitiser comes in the form of a chlorine gas that dissolves into the water.  The process does not consume the salt, as when the chlorine breaks down, it turns back into salt, so creating a cycle.

Swimming Ponds:

For those who like to be close to nature, swimming ponds are the way forward.    If the body of water is large and deep enough, clear, clean water is the naturally occurring state in ponds and lakes.  Swimming ponds are designed with these features in mind and are a prime example of how we can copy nature’s ideas.  Usually, a swimming pool has chemicals or treatments added to kill micro-organisms in the water such as phytoplankton (microscopic single-celled algae, which can make the water go green, if enough is present) and bacteria.  However, this isn’t the case in a swimming pond, where micro-organisms exist together in equilibrium and actually undertake the cleaning of the pool.  The fundamental purpose of a swimming pond is to be as naturally clean, clear and healthy by harnessing the natural properties of plants and micro-organisms that filter water.

Swimming ponds are made up of several parts.  The main filter is the body of water, like it would be in nature.  In nature, the water is constantly being filtered by microscopic life forms.  To keep the nutrient levels to an essentially low level, so that single-celled algae is kept under control by zooplankton and to prevent the growth of blanket weed (string algae), water is also filtered through shingle and other natural means using a small pump.  As well as being pleasant to look at, plants, as they grow, take nutrients from the water, so by keeping the levels of key nutrients low and balanced, algae cannot grow.  The result is swimming water that is healthy, clean and clear.

It is also possible to have a swimming pond indoors.  The principle of filtering the water is the same as outdoors: to be natural and to keep the nutrient level balanced and low.  As the swimming pond is indoors, some additional factors have to be taken into account in the design stage, such as using appropriate materials for high humidity, enough light for plants present and being the right temperature for filtration to work effectively.

Natural Swimming Pool Filter System


Ozone is usually associated with global warming, however, it is also a powerful and effective highly active form of oxygen that is hundreds of times more efficient than chemical treatments such as chlorine for sanitizing swimming pools.  The urea and ammonia responsible for chloramine production in the swimming pool is oxidised by the ozone.  As these pollutants are reduced, THM (trihalomethanes are formed as a by-product predominantly when chlorine is used to disinfect water for drinking) levels are also reduced.

The ozone is generated on site and as it dissolves in the swimming pool water, it kills all bacteria and viruses, which leaves the water crystal clear and free from smell and taste.  Ozone can be produced in two ways.  Ultraviolet radiation (UV) is used for low doses of ozone and creates the ozone by passing air over a specially dosed ultra-violet lamp.  A corona discharge generates ozone by passing a stream of air through an electric arc and this process is suitable for higher volumes of ozone.  The ozone is then mixed with water from the swimming pool filter and the mixture is held in a tank for a predetermined time to allow for it to react with the impurities in the water and allow any excess ozone to separate from the water.  The excess ozone, which has now been converted into a gas, is destroyed and converted back into oxygen and released back into the atmosphere.

Even though the ozone sanitises the water, the water itself cannot clean itself and as soon as it comes into contact with bathers will start to become unsanitary.  That is why a low dose of chlorine is added to keep the water clean whilst in the actual pool.  Benefits of an ozone pool are that even though chlorine is still used, the levels are vastly reduced, thus reducing any irritation caused to the swimmer.  By-products, such as THM levels and algae are better controlled and savings in power are reduced.

Ultraviolet Light (UV)

Ultraviolet light is commonly used in a concentrated form for sunbeds and lights in the entertainment industry; it is also used for sanitising swimming pool water too.  The UV is generated by two types of lamp (similar to that of a fluorescent tube), low pressure and medium pressure.  The swimming pool water flows from the filter through a stainless steel chamber, where the UV lamp is located.  The time in which the water spends in the chamber is calculated, so that it receives the correct dosage of UV to sanitise.

UV is highly effective at oxidising organic species in the water and inactivating bacteria and viruses when produced by a medium pressured lamp.  Because UV disinfection is chemical free, it is ideal for attacking the vital DNA of bacteria directly, including such parasites like cryptosporidium or giardia, which are resistant to chemical disinfectants.  Chloramines are also reduced by a variety of ways by the UV.

The main benefits of having a swimming pool treated by UV is that chlorine and chloramines levels are safely reduced and therefore so is the level of chlorine consumption.  Due to the fact that fewer chemicals are used, the water and air will be of a purer quality and thus any side effects to the swimmer will be reduced.  The lifespan of the swimming pool and building will also increase, also due to the decrease in chemicals used.

Like ozone, water treatment with UV means that the water is sanitised before re-entering the swimming pool, but chlorine has to be added to keep the water clean, whilst in the swimming pool itself.

Each individual treatment has its pros and cons.  What might be right for you or your swimming pool might be wrong for the next person.  In the next blog, we continue to look at the other possibilities to that of chlorine, including the prospect of using silver.

Pool Or Freedom?

Pool Or Freedom?

Westbrook Seals

The question of what is preferential, open water swimming or swimming in a pool has been at the back of my mind for some time now.  My own swimming experience is virtually pool swimming, with the occasional sea swim whilst on holiday.  The taste of salt water and the burning sensation if you swallow it does not appeal to me in the slightest; however, chlorine doesn’t bother me if I get it in the mouth, but is incredibly drying on the skin.


Serious swimmers seem to increasingly prefer open water swimming, even in the depths of winter.  Time and time again the same reasons are being cited as to why this is so: the freedom of not being in a confined space, not having to worry about lane etiquette and not being coated in chlorine.  Each swim in an outdoor environment is individual; the conditions are never exactly the same and the scenery changes due to the seasons of the year.  There are no entrance fee and lane ropes.  Which leads onto the second problem of swimming in pools, lane etiquette.  Open water swimmers will swim in pools, but not necessarily through choice, partly due to the fact that casual swimmers don’t follow lane rules.  I have seen photos of swimmers who have deep scratches to their bodies done on purpose by other adult swimmers who don’t like being overtaken by a better and stronger swimmer.  The Daily Mail published an article in early January revealing that scientists have found insect repellent, caffeine and flame retardant chemicals in public pools.  Also small children are notorious for having accidents and even though healthy urine is regarded as sterile, some elements of urine, such as urea and uric acid, once mixed with chlorine, can be potentially hazardous.  So how do other chemicals such as caffeine get into swimming pool water?  The simple answer is that a lot of swimmers do not understand or choose not to understand swimming pool etiquette.  There is a reason why you should go to the toilet, blow your nose and shower before swimming - it keeps the water clean.  The everyday chemicals that we choose to use on our skin are transferred into the swimming pool along with sweat, skin cells and faecal matter.

Aqua Duck Water Coaster On The Disney Dream


Swimming pools do have their benefits though.  They are constantly supervised and risk is kept to a minimum.  Open water swimming is generally frowned upon by the Health and Safety brigade who tend to focus on incidents caused by swimmers who are not experienced in outdoor swimming, such as being drunk.  As a swimming teacher, I do tell my swimmers not swim in open water due to the fact that you don’t know what lies beneath the surface. Learning to swim or practicing technique/drills are best undertaken in the pool, as the conditions can be strictly controlled and are predictably constant throughout.  Long distance training in the depths of winter isn’t possible as hypothermia will set in after ten minutes during an open water swim where the temperature is only 4 or 5 Celsius, however temperature is not an issue in a pool.  There is also the problem with how clean the water is with open water swimming.  Waterways shouldn’t be as polluted as they once were, but individuals and private companies sometimes fly tip into convenient locations and of course, there are naturally occurring pollutants.  Swimming pools provide a variety of classes that simply wouldn’t be possible in open water – aqua aerobics in Loch Ness?  Where would you plug in the stereo system?  These classes can also inspire non-swimming participants to learn to swim, which then opens up a whole different world of possibilities.  Swimming pools are synthetic, but the way they are built and the facilities that are provided along with them (aqua flumes, wave machines, etc.) can be a lot of fun.  Pools do not have to be treated with chlorine, so if chlorine doesn’t suit you, try and see what is available to you in your area.

At the end of the day, it doesn’t matter how you like to swim, as long as you enjoy it and keep safe.  There are pros and cons to both environments, but life is like that anyway!

For more information on open water swimming, please visit