Chlorine is used in a wide range of applications, not just swimming pools. It is a good pesticide or sanitiser. It is produced commercially from electrolysis of salt water (sodium chloride) similar to a salt chlorinator or the ocean, which produces more than man ever has every day.
Chlorine comes in a number of forms including liquid, gas or solid. Calcium Hypochlorite is the standard granular chlorine used in swimming pools. Liquid chlorine or Sodium Hypochlorite is actually weaker with 1 litre being equivalent to 1 cup of granular chlorine. Liquid however is faster acting as it is already dissolved in solution. Pools that use liquid chlorine a lot will find a rise in their Total Dissolved Solids (TDS) level which is due to the salt content.
The other common forms of chlorine are as a stabilised granule or tablet, most commonly Dichloroisocyanurate (Dichlor) or Trichloroisocyanurate (Trichlor). Dichlor has 2 chlorine atoms to every molecule while Trichlor has 3 making them a more highly concentrated chlorine. These two chlorine compounds contain stabiliser (isocyanuric acid) and when dosed in the pool the chlorine and stabiliser must separate in reaction. If there is too much stabiliser or too much chlorine then the reaction that splits these chemicals does not properly occur. This is what is more commonly known as ‘chlorine lock’ and does not allow enough active chlorine into the water. Adding unstabilised chlorine will allow the reaction to occur and allow the tied up chlorine to be broken up and become active. This is why you should not solely rely on stabilised chlorine as a pool sanitiser. Adding stabiliser separately and using normal chlorine will not only be just as effective but it is also significantly cheaper. It is recommended on the packaging of these products not to use them if the stabiliser level is over 50mg/L. Above this you should use an unstabilised chlorine.
Chlorine residue, from granular chlorine, is the result of mixing the chlorine with lower grade materials. Pool chlorine is usually 65% chlorine. The compounds that make up the extra volume are what have the greatest effect on price. Cheaper chlorine will be mixed with lower grade compounds resulting in anywhere up to 30% of the granules not dissolving, while better quality chlorine can be up to 99% – 99.9% soluble.
Weak chlorine is also known as bleach. Be careful handling chlorine, as it will destroy clothing.
Chlorine can be neutralised. Sodium Thiosulphate will reduce chlorine levels dramatically and the no.4 test solution is actually 10% sodium thiosulphate. We would not normally add this to swimming pools unless absolutely necessary. Too high chlorine is not usually a problem and chlorine will dissipate with sunlight. As a warning in fibreglass or vinyl pools suddenly reducing the chlorine level can exacerbate staining.
What about the alternatives? There are a number of alternatives for chlorine advertised on the market however not all of them are as effective a disinfectant. The Australian Pesticides and Veterinary Medicine Association (APVMA) regulates approved pesticides or sanitisers. Their list of approved pesticides currently only includes chlorine, bromine and hydrogen peroxide. This means that chlorine should be used with most of these alternatives anyway to ensure the water is sanitised properly. Bromine is actually a better sanitiser than chlorine and is primarily used in spas, where chlorine evaporates due to the higher temperatures. Bromine however can also irritate skin and can have an overpowering odour. It also accumulates and can build up a high residual level in spas over the years. Bromine is also very acidic and affects pH greatly. This can lead to heater corrosion and the pH should be monitored regularly. A high Bromine level can also cause test kits to show false pH readings, so always use a few drops of neutraliser solution. Spas should be drained every four months for health reasons, although brominated spas should be emptied every few weeks. As spas are significantly smaller than a pool they can be effectively sanitised using chlorine or bromine alternatives.
Only 15 major elements makes up 99.5% of the human body and chlorine is the 10th. A different 15 major elements make up 99.5% of the earth’s crust, including air and water, and chlorine is the 11th. It is one of the most common elements in nature and is even more plentiful than carbon. The oceans release approximately 3 million tonnes of methyl chloride into the atmosphere each year, while in addition 5,000 – 15,000 million tonnes of inorganic chlorine is thrown into the atmosphere as sea mist (between 3-35% of this remains in the atmosphere, while the rest will return to the sea). [Chlorine Online]
85% of medicines, including many life saving drugs, are made using chlorine chemistry. 98% of western Europe’s drinking water is sanitised with chlorine. 25% of medical devices contain chlorine, including blood bags, tubing, heart catheters, prosthetics and x-rays. Chlorine is required to produce protective safety equipment, communications equipment and microprocessors, including telephones, radios and computers, sporting equipment, including soccer balls, surfboards, and skis, house construction, including window frames, plumbing, paint, glue and concrete, and in many consumer products and cosmetics. [Chlorine Online]
Greenpeace stated in 1994 that ‘Of more than a hundred chlorine containing organic materials, the carcinogenic effect has been proven’. This is true but this is because there are no carcinogenic materials only carcinogenic doses as everything is a carcinogen, depending on the dosage ingested. Large studies overseas have shown that chlorine and it’s use in the manufacture of PVC and other products is actually less dangerous than most alternatives, even natural ones. A study conducted in the Netherlands actually looked at chlorine and it’s associated risks and found it to be an incredibly safe and healthy product, which is why it is used worldwide. [The Chlorophiles]
As you can see, chlorine is a very safe and abundant chemical which while toxic in it’s purest form, it is safe in the forms we commonly use it today. By chlorinating your pool or spa you are killing all bacteria and putting oxygen into the water. This is what makes is perfectly safe to drink, shower and swim in.
See: The Chlorophiles, APVMA, Chlorine Online