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.
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.
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.
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.
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.