Earn 25 credits towards the Pool & Hot Tub Council of Canada’s ( PHTCC’s) Industry Trade Certification Program by completing the quiz. 

Like water, chlorine is also a very reactive chemical. Anytime chlorine and water meet very rapid reactions take place as follows:

Cl + H2O = Hypochlorous Acid (HOCl)

HOCl is the secret agent that does the killing of micro-organisms. Water, almost instantaneously, begins its job of ionizing and hypochlorite ions (-OCl) are produced.

Cl + H2O = HOCl + -OCl

When it comes to effectively killing germs and protecting swimmers, HOCl is the muscle providing 99 per cent power. The –OCl is weak, as it only provides one per cent power. Therefore, since the sole purpose of chlorine in pools is to keep swimmers safe from diseases, it goes without saying that there needs to be a majority of HOCl present.

What is the best way to accomplish the effective level of killing agent chlorine? Just as in life, for water chemistry to work, there must be balance. The presence of HOCl in pool water is dependent on where the pH level lies. High pH will mean a minimum of strong killing HOCl, while lower pH will give more killing agent HOCl. For instance, if the pH level is 8 there is only 24 per cent of HOCl killing agent in the water. There is 66 per cent HOCl in the water at a pH of 7.2. At the ideal pH level of 7.5 there is 50 per cent of both the HOCl and –OCl. Remember everything is about balance.

Which type of chlorine should be used?

After its immediate reaction of disinfecting and oxidizing, an initial byproduct is left behind in the water. The byproduct left behind, however, is dependent on the type of chlorine being used as the primary sanitizer.

Inorganic

Chlorine gas

Calcium hypochlorite (cal hypo)

Sodium hypochorite

Organic (Stabilized)

Trichlor

Dichlor

Cal hypo leaves calcium as the initial byproduct in the water. In fact, (0.45 kg [1 lb] of cal hypo increases the hardness by 4 parts per million [ppm] in 37,854 L [10,000 gal] of water). Stabilized forms of chlorine contain cyanuric acid (CYA). For every 0.45 kg (1 lb) of Trichlor, there will be 7 ppm of CYA left in 37,854 L (10,000 gal) of water.

Liquid chlorine is sodium hypochlorite that leads to sodium chloride being left behind as a byproduct. This causes an increase of total dissolved solids (TDS).