Mineral Pools, are they chlorine free?
With the craze of ‘mineral’ pools that has hit the pool industry over the last 5 or so years, its important to understand how it all works.
Let’s start with where it all began, the backyard salt (sodium salt) chlorinator. All you had to do was throw in bags of salt and walk away. Ahhhhh that salt water beach feeling! No more manually dosing the pool with chlorine sanitiser either.
Then came along the ‘Mineral’ salt (blends of salts and trace elements, magnesium + potassium + calcium + zinc + copper + iron) chlorinator. It’s driving force the ability of the minerals and trace elements to be dermally absorbed into the skin while swimming to alleviate muscle aches, bring oxygen to the body’s cells, alleviate eczema, relax the nervous system and even soften the water.
Sodium salts or magnesium salts alone are NOT a sanitiser! However, they are both used to make chlorine (sodium hypochlorite), which is a sanitiser.
So how do we make chlorine out of salts? Electrolysis!
The process involves passing salt water (which is a good electrical conductor) through what is called a ‘cell housing’, which houses a cell, made of a series of flat titanium plates coated with iridium and ruthenium and aligned parallel to each other in the cell housing. Electricity is applied to these titanium plates, which separates the chemical bonds of the salts (sodium chlorine/ magnesium chloride) and in the process creates chlorine gas (Cl2), hydrogen gas (h2) and sodium hydroxide (NaOH). The chlorine gas reacts with water (H2O) to form Sodium hypochlorite.
For the chlorinators to work they require specific levels (anywhere from 2500ppm up to 8500ppm) of Total Dissolved Solids (TDS), which a big component of is achieved by the addition of salts. If there is not a sufficient level of TDS the chlorinator will not produce chlorine. If the level of TDS is too high the chlorinator will shut off in order to prevent overload on the cell.
Fresh water chlorination is a whole new kettle of fish! These systems run with very low TDS levels, as low as 1200ppm. They don’t require salt or minerals to be added to the water to produce chlorine, as typically once the pool is filled with water and balanced with chemicals (calcium, alkalinity, acid) the TDS level is sufficient for operation of the fresh water chlorinators to start producing chlorine.
It is a good time to note that a sanitiser level maintained by salt, mineral or fresh water chlorinators (2-4ppm) will not remove inorganic and organic waste products (food source for bacteria), nor destroy chlorine by-products (irritants to the skin and eyes) and does very little for chlorine resistant parasites such as Cryptosporidium and Giardia.
Written by John Morrison BSc
- Electrolysis; production of sodium hydroxide, chlorine and hydrogen. Science encyclopedia. 2019.
- Swimming Pool urine combines with chlorine to pose health risks. Purdue University. 2014.
- Cryptosporidiosis as threatening health problem: A review. National Centre for Biotechnology Information. 2013.
- Facts about Giardia and swimming pools. Centers for Disease Control and Prevention. 2017.