What is a Chlorinator? | Convenience, the experienced pool owner’s choice

Published by Swimming-Pool-Expert on June 28th, 2011

How do Pool Chlorinators Work?


Chlorine in one form or the other has been in use in a wide variety of industrial applications for a long time, and in that time we have come to understand it extremely well. Although there are some people who believe chlorine in pools poses a safety hazard, clinical studies have found no such link – either to swimmers or the environment. This is why nearly every pool in South Africa continues to employ chlorine as a free-ranging antibacterial agent, keeping the water clean and clear and maintaining an essential level of purity for recreational use. If you own a pool, however, you know that regulating chlorine can represent something of a hassle.

The reason for this is actually quite simple: chlorine breaks down over time when exposed to sunlight. Although hypochlorous acid – the essential byproduct when you add chlorine to the pool – is mostly used to destroy unwanted particles, it can also react with ammonia and nitrogen compounds to form chloramines. These inert compounds are essentially harmless, and they offer little protection against bacteria in the water. Further complicating matters is the fact that chlorine can also be broken down by the sun itself, decreasing its effectiveness against bacteria, mold and algae. This is why maintaining proper chlorine levels can be a daily chore, one rendered even more frequent in the event of parties, thunder and rain.

Pool chlorinators are the most common response to fluctuating levels. These tend to come in a variety of chemical forms under a number of brand names, but generally they can be divided cleanly into a few major categories. Each offers advantages and disadvantages, including effectiveness and potential hazards. Chlorine is, after all, a terribly corrosive chemical, so it’s important to deploy with a healthy level of respect. Anything less than proper precautions and you could find yourself stuck with chemical burns, lung damage or worse – terrifying outcomes for such a mundane task.

The most dangerous version of chlorine is also the most effective – chlorine gas. Introduce the gas into any pool filtration system and you can expect immediate results. The problem is that such results tend to cause problems with the pool’s pH, creating a corroding environment that is highly unsafe for recreation. Large amounts of basic chemicals are usually required to pull that pH back into a safe range, though chlorine gas may still cause a host of health problems before it even reaches the pool. Breathe in pure chlorine or anything close to it, for instance, and you may quickly fall unconscious and die. It may not surprise you to learn that pure chlorine gas is hardly ever used for home pools anymore.

Today a number of homeowners in Europe and the USA use so-called liquid chlorine instead. This looks and smells similar to bleach, and it’s created by bubbling the pure gas through caustic soda. Results can be swift and impressive, as with the gas itself, which is why liquid chlorine is often favoured as a method for shock. Everyday use has fallen by the wayside a bit for the same reason, however – like chlorine gas, liquid chlorine can increase pH.  Such health risks and high expense have made this solution unpopular, especially since considerable quantities of base are required to mitigate the unwanted effect. Thankfully there are some safer and more convenient ways to deliver chlorine in a hurry.

Of these, the most popular may be so-called “stabilized tri-chlor,” the version most often recommended by pool experts. The compound usually comes as a powder (e.g Clarity Micro Granular Chlorine), though you can also get slow-release “tablets” that will maintain an even level over several hours. Homeowners often favour this version because it releases slowly, maintains a sound pH in the system and comes with an extra sort of sunscreen – cyanuric acid– that keeps the chlorine effective several hours longer than its non-stabilized counterparts. That means you save time, money and headaches by trusting a single advanced compound to lighten your load.

Chlorine is essential to maintaining the safety of standing water. Experiment with the products you find until you can keep pH, alkalinity and chlorine levels within acceptable limits on a daily basis.

Sanitizing a pool with a salt water chlorinator uses a similar technique as sanitizing the same pool with other chlorine forms. The most common form of chlorine used for manually sanitizing pools is either granular chlorine, or sodium hypochlorite (sometimes called liquid chlorine). Commercial pools which do not use a salt chlorinator use a variety of forms of chlorine, including chlorine gas.

Note that calcium hypochlorite contains abdout 65% chlorine (e.g. HTH),  trichlor combinations contains approximately 90% chlorine, but the chlorine produced by a salt water chlorinator is 100% chlorine.

The chlorine produced by a chlorinator is exactly the same element (chlorine) as is contained within sodium hypochlorite and calcium hypochlorite. In other words, the active sanitizing agent for all of these methods is the same….chlorine.

Mass chlorine production in huge chlorine factories uses exactly the same basic technique as is used by a chlorinator. This technique involves the passage of electric current through salty water to produce chlorine gas at the positive electrode (anode).


The chlorine produced by a salt water chlorinator is a product of salt water. The process may be explained in chemical terms by the formula below.

NaCl + 2H2O HOCl + ClOH + NaOH

(Salt + Water + Electricity produces Hypochlorous acid and Hypochlorite ions + Sodium Hydroxide.)


The formula does not mention chlorine gas, because the chlorine dissolves immediately as part of the reaction. (The elemental chlorine gas produced at the anodes in the electrolysis process dissolves immediately into the water to form hypochlorous acid and hypochlorite ions.)

This is the same chemical reaction as occurs at commercial chlorine manufacturing facilities.

It is the hypochlorous acid and to a lesser extent, the hypochlorite ions that perform the sanitizing function in the swimming pool.

The cell produces elemental chlorine gas in the water, and the chlorine produced is exactly the same as other types of chlorine used for swimming pool sanitization. Regardless of whether the chlorine comes from the electrolytic action of a chlorinator cell, or from the chlorine contained in granular chlorine or liquid chlorine, the chlorine dissolves into the water to form hypochlorous acid and hypochlorite ions. It is actually these two components which are the active sanitizers in pool water. Hypochlorous acid is a strong sanitizer and hypochlorite ions are a weak sanitizer. It is important that the pH of the water is correct to ensure a high proportion of hypochlorite acid, and therefore, the most effective sanitizing of the pool.


The reasons why sanitizing using a salt water chlorinator is better than other techniques are as follows:

a) Salt water chlorinators manufacture and deliver chlorine to the swimming pool automatically. The pool owner no longer needs to purchase, transport, store or manually add chlorine as part of their routine maintenance.

b) Not only is the water passing through the cell subjected to the sanitizing effect of the chlorine being introduced into the water, but as the water passes between the positive and negative electrodes, the bacteria, and algae are subjected to a very strong electric field which oxidizes these contaminants. These contaminants and others, including sunscreen, lotion, and body oils, etc are doubly attacked when using a chlorinator cell. They are destroyed not only by the chlorine in the water, but also by the electric field within the electrodes.

c) Salt water chlorinators manufactures and delivers chlorine to the pool in a constant and controlled manner. Because a salt water chlorinator is part of the filtration system, the sanitizing takes place every time the filtration system is switched on. There is less reliance on the human factor.

d) Say good-bye to red stinging eyes, skin irritation and harsh chemical odors. In general, whenever swimmers enter chlorinated water, chloramines are formed. This occurs because the body wastes, perspiration and skin oils all contain amine compounds which react with the chlorine in the water. If the chlorine only partly oxidizes (destroys) the amine compounds, “chloramines” are formed.

Chloramines are unpleasant smelling substances which sting the skin, cause eyes to become red and sore, and in extreme cases (high concentrations and allergic individuals), can cause skin rashes.

The major scientific benefit offered by salt water chlorination in the sanitizing process is that not only is there a sanitizing action in the swimming pool resulting from the free chlorine residual in the water, but there is a far more powerful sanitizing action which takes place in the cell itself.

As the water passes between the electrodes, the chloramines in the water are destroyed as they pass through the cell. Only a salt water chlorinator can destroy chloramines in this way.

e) When a salt water chlorinator is used, there is more than an even dosing rate of chlorine. If for example the filtration system is operated 8 hours per day while the bathers are in the water, then the water is being sanitized continuously during the 8 hour period. The chlorine level remains at a satisfactory reading while the bathers are in the water.

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