Chlorine is the most commonly used product for treating swimming pool water. It is also the most economical treatment compared to bromine and salt. Its disinfectant properties eliminate all micro-organisms in the water and it is an effective algaecide. Are you unsure about which treatment to choose for your swimming pool? Read this article to find out everything you need to know.
Chlorine is a chemical element that belongs to the halogen group, along with fluorine and bromine. It is both a disinfectant and an oxidant, playing an essential role in maintaining healthy, balanced water. Like bromine, it is a disinfectant and a preventive algicide. The chlorine level varies depending on the pH of the pool. If the pH is too high (pH>7.8), chlorine becomes ineffective.
It's the transformation of chlorine into chloramine (in contact with body pollutants) that creates this characteristic odor. In other words, it's possible to smell the quality of chlorine-treated water. If your pool or spa smells of chlorine, it's because the water is fairly polluted.
Chlorine for swimming pools comes in several forms: liquid, pebble or powder. The disinfecting power of chlorine does not change according to the type of packaging, but the speed at which it is diluted in the water does, and therefore its effectiveness over time. So it's perfectly possible to use several forms of chlorine, depending on your needs and the problem at hand.
Chlorine tablets can be placed either in your pool's skimmer or in a floating dispenser (for above-ground pools). When in contact with water, the tablet gradually dissolves. Their slow-release action serves to maintain chlorine levels. This is the ideal form for regular maintenance of your pool or spa. Depending on the number of bathers and the filtration time, chlorine tablets should be added once or twice a week. There are also tablets for shock chlorination (at the start of the season or to quickly treat a water quality problem), which act very quickly.
Powdered chlorine dissolves quickly in water and acts rapidly. It is often used as a shock treatment to treat green algae or when restarting your pool after winter storage.
Liquid chlorine has the reputation of being a little more difficult to dose and handle. The pool surround must be protected to prevent discoloration (watch out for splashes), and bathers must be prevented from entering the pool for several hours after pouring the product into the water. Liquid chlorine is rarely used by private individuals (unless their pool is equipped with a dosing pump). It is more commonly used in public pools.
There are two commercially available types of chlorine for disinfecting your pool or spa water, stabilized chlorine and non-stabilized chlorine.
It has a high disinfectant power, but UV rays can significantly reduce its disinfectant power within a few hours. After 3 hours' exposure to the sun, 5% of unstabilized chlorine and 70% of stabilized chlorine remain in your pool. You can top this up with a stabilizer at the start of the season. This product is more commonly used by spa owners (who have a cover) and indoor pool owners.
As its name suggests, it contains a stabiliser, cyanuric acid, which protects it from UV rays. It is the most commonly used form of chlorine for swimming pools due to its convenient and comprehensive use. However, care must be taken as the stabiliser (which must be between 30 and 50 mg/L) accumulates in the water and blocks the disinfecting action of the chlorine. Furthermore, there is no way to reduce it except by emptying part of the water from the pool. Stabilised chlorine must therefore be dosed with great precision and measured weekly.
Chlorine is a very powerful chemical that must be handled with care: gloves, masks and goggles (for liquid chlorine) must be worn. It must be stored out of the reach of children and animals, in a dry, well-ventilated place.
| Criteria | Unstabilised chlorine | Stabilised chlorine |
| Benefits | Rapid and powerful disinfection | Easy to use, durable, effective in sunlight |
| Drawbacks | Disappears very quickly in sunlight, requires a stabiliser | Accumulation of stabiliser, which can block the action of chlorine |
Depending on the measurement tools used, they do not all analyze the same chlorine.
First of all, you need to know that there are several types of chlorine: total chlorine, free chlorine, potential chlorine and active chlorine. When chlorine comes into contact with water, it is transformed into active chlorine and potential chlorine.
When chlorine turns into chloramine (also known as combined chlorine), on contact with organic matter (sweat, dead skin, etc.), or depending on water temperature and pH. Chloramines are responsible for the specific odor of swimming pools.
Not every chlorine molecule is responsible for or active in disinfection. Active chlorine is the only chlorine active in water disinfection. The more chloramines a water contains, the less active chlorine it contains.
A chemistry expert explains the differences between the types of chlorine.
Because some chlorines are not involved in water disinfection (total chlorine, free chlorine and potential chlorine), make sure that the measuring system you choose analyzes free chlorine, as it is this measurement that gives you the right information on water health.
Chlorine treatment offers many advantages. Firstly, it's a powerful algaecide and disinfectant that's easy to use. It's also the most economical product, compared with other water treatments such as salt and bromine. Finally, it's available everywhere (supermarkets, specialist stores, etc.).
The smell of chlorine, or more precisely chloramine, can be a real turn-off for some people. When poorly dosed, it can cause irritation to the eyes and mucous membranes, as well as discomfort to the skin. Secondly, it is important to note that chlorine is less stable when exposed to UV rays. If your pool is particularly exposed to the sun, it may be better to consider a salt treatment, which would be more suitable. Finally, the chlorine level varies according to the pH, so this is a parameter that needs to be monitored closely and regularly to maintain good water quality.
The treatment of swimming pool and spa water is undoubtedly the most common type of treatment. Economical and practical, chlorine is widely recognised for its effectiveness in disinfecting water. However, it remains a chemical product that must be handled with great care to protect the health of bathers.