During oxidation, electrons are transferred between hypochlorous acid and its target. Nitrogen and various nitrogenous compounds are common targets for chlorine as they readily react with it. To prevent these nitrogenous compounds from continuing to react with the free chlorine necessary for proper sanitization, a weekly shock can be administered for regular maintenance. Shocking the pool after rainstorms or heavy use also proves effective. Additionally, promptly removing visible debris like leaves, pine straw, or tree limbs can prevent major issues and chlorine depletion. Utilizing regular maintenance shocks to prevent contaminant accumulation will help avoid costly battles with super-chlorination or water dilution.
Water balance: pH and chlorine equilibrium
Maintaining balanced water is crucial not only for safeguarding pool surfaces and equipment but also for optimizing chlorine’s effectiveness. When chlorine is added to the water, it breaks down into hypochlorous acid (HOCl) and hypochlorite (OCl-). HOCl, which is essential for sanitization and oxidation, performs most efficiently in neutral environments with a pH range of 7.4 to 7.6.
HOCl ß à H+ + OCl–
A lower pH in the water favours the production of more HOCl, while a pH above 7.6 shifts the equilibrium towards generating more OCl-, which is significantly less effective—about 80 to 100 times weaker in its sanitizing capabilities. OCl-’s weaker negative charge repels negatively charged micro-organisms, leading to less effective elimination. When choosing a chlorine form, such as trichlor, calcium hypochlorite (Ca[ClO]₂), liquid chlorine, or saline, it is crucial to consider their varying impacts on the water’s pH.
| pH | % HOCl | % OCl– |
| 7 | 76 | 24 |
| 7.2 | 66 | 34 |
| 7.5 | 50 | 50 |
| 7.8 | 33 | 67 |
| 8 | 24 | 76 |
Alkalinity effects on sanitization
Maintaining the proper total alkalinity (TA) range is crucial for ensuring a balanced pH level. If the TA falls below 40 parts per million (ppm), it can lead to pH fluctuations that are challenging to correct. Low TA levels can cause the pH to decrease, negatively affecting swimmers’ comfort and causing damage to pool surfaces and equipment.
The impact on alkalinity becomes significant when considering chlorine-based sanitization methods. Both salt chlorinators and sodium hypochlorite introduce a byproduct called sodium hydroxide (NaOH). If not appropriately balanced with acid, this can create a more alkaline environment, leading to issues like cloudy water or conditions that promote harmful scale formation.
