Swimming Pool Blog
by Mark Garcia, Nov 7, 2019
Super-Chlorination vs. Hyper-Chlorination
For anyone who owns a pool, and for many who don't - shocking the pool is a familiar term.
Shocking the pool with granular chlorine is raising of free chlorine levels to such a high level that every living thing in the water is killed by cell disruption. The process is not unlike a lightning bolt ripping through the water, and perhaps that's why we call it shocking the pool.
Oxidation is a term that is also used to describe raising the level of sanitizer in the pool. Granular chlorine, (or non-chlorine shock) oxidizes the contaminants in the water, by attacking the cell walls of pathogens, algae and bacteria. Oxidation begins immediately when granular or liquid chlorine is added to water.
Add enough pool shock to the water, and you will reach what's known as "breakpoint chlorination", a threshold beyond which survival of any contaminant is unlikely. This is when the level of sanitizer is greater than the sanitizer demand, and free chlorine levels can rise, unimpeded.
Super Chlorinating the water is not the same as shocking the pool to reach breakpoint chlorination. A true 'shock' of the pool requires at least one pound of pool shock per 10,000 gallons, or more specifically, a level of chlorine that is 10x the level of combined chlorine, when one is shocking to remove combined, or chloramines.
Super Chlorinating the pool is less-than, a full shocking of the pool. If shocking the pool was to raise the chlorine level to 10 ppm for instance, super-chlorinating would be raising it to 5 ppm. It is 'Super' because it is more than the normal, everyday dose, but is not generally considered to be a full shocking of the pool.
Super chlorinating is raising the chlorine level 3-5x the normal levels, to act as a booster, to kill algae that may be in the beginning stages, or to deal with cloudy water or other water conditions. Most often, a pool owner may super chlorinate the pool when the chlorine level is found to be near zero - but there is no need for a full-on shocking of the pool. No full-blown algae bloom, or detectable levels of combined chlorine, but rather an extra dose 'just to be safe'.
You may not have heard the term hyper chlorination before, and some of you may think I'm having some fun with terminology, making this stuff up as I go along. But no, hyperchlorination is a real term, and can be defined as maintaining very high levels of chlorine for extended periods of time.
Some pathogens such as Cryptosporidium or Legionella are somewhat chlorine resistant, and can take long periods of time, with high levels of sanitizer, for complete eradication. Fecal accidents in pools and spas, or water left stagnant for extended periods of time may require extended-duration shock treatment, or hyper-chlorination.
Hyper chlorination as defined by the CDC is raising the level of chlorine in the water to 30 ppm, and maintaining the level for at least 8.5 hours. However, it depends on the level of contamination in the pool, and also depends on the use of, and level of cyanuric acid in the pool water. Levels of up to 50 ppm may be required in some cases, and for as long as 36 hours in extreme cases.
- For pools that use cyanuric acid to protect chlorine from the sun, even higher levels of chlorine are needed to achieve effective hyper chlorination. Cyanuric Acid (aka chlorine stabilizer) has a suppressive effect on chlorine, which can require a much higher chlorine dose, to counteract the cyanuric acid. A ratio of 20:1 cyanuric acid to free chlorine has been suggested, or that free chlorine levels should be 7.5% of cyanuric acid levels.
- High pH levels also have a suppressive effect on chlorine efficacy or potency. Be sure that the pH level is a stable 7.2-7.4 before hyperchlorination. Total alkalinity levels that are too low or too high can make it hard to maintain pH in the 7.2 to 7.4 range for effective hyperchlorination. Check that both total alkalinity is 80-120 ppm and pH levels are 7.2 to 7.4 before attempting to hyper chlorinate a pool.
- After the period of hyper chlorination has passed, free chlorine levels can remain too high for swimming for many days. To restore safe chlorine levels, the Illinois Dept. of Health suggests using Sodium Thiosulfate, as a chlorine neutralizer, to lower levels of free chlorine below 5 ppm.
- Lower levels of chlorine may be suitable when supplemental sanitizers are also used, such as UV radiation, ozone treatment, or the combination of both with a hydroxy radical treatment, known as AOP or advanced oxidation process.
- Proper and continuous water testing is crucial during a hyper chlorination treatment. A high-level DPD test kit that can accurately test for very high chlorine levels is needed, like the Lamotte ColorQ or Taylor FAS-DPD test kits.
- Use a non-stabilized form of chlorine for hyper chlorination, such as sodium hypochlorite or calcium hypochlorite. Do not use chlorinated isocyanurates or non-chlorine monopersulfate oxidizers.
Thanks for Reading!