Chlorine as a Sanitizer for Swimming Pools

Chlorine is the chemical most often used to keep swimming pools free of algae as well as bacteria that can be hazardous to humans.

Chlorine kills bacteria though a fairly simple chemical reaction. The chlorine solution you pour into the water breaks down into many different chemicals, including hypochlorous acid (HOCl) and hypochlorite ion (OCl^–). Both kill microorganisms and bacteria by attacking the lipids in the cell walls and destroying the enzymes and structures inside the cell, rendering them oxidized and harmless. The difference between HOCl and OCl^– is the speed at which they oxidize. Hypochlorous acid is able to oxidize the organisms in several seconds, while the hypochlorite ion may take up to 30 minutes.

The levels of HOCl and OCl^– vary with the pool’s pH level. If the pH is too high, not enough HOCl is present and pool cleaning can take much longer than normal. Ideally, the level of pH in the pool should be between 7 and 8.  A pH of 7.4 is ideal – as this is the pH of human tears and Chlorine is effective at this pH level. Once the HOCl and OCl^– are done cleaning the pool, they either combine with another chemical, such as ammonia, or are broken down into single atoms. Both of these processes render the chlorine harmless. Sunlight speeds these processes up. You have to keep adding chlorine to the pool as it breaks down.

While the bacteria-killing properties of chlorine are very useful, chlorine also has some side effects that can be annoying to humans, and possibly even hazardous. Chlorine has a very distinctive smell that most find unpleasant, and some find overwhelming. There is also the “itch factor” — chlorine can cause certain skin types to become itchy and irritated. The hypochlorite ion causes many fabrics to fade quickly when not rinsed off immediately after exiting the pool. This is why your swimsuit looks faded and worn so early in the summer.

SUMMARY:-

1. Rather put DISSOLVED chlorine into pool in the late afternoon or when the pool is in shade.
2.  Rather put in “SMALL” quantities of chlorine “MORE OFTEN” than “LARGE” quantities “LESS OFTEN” because if you have put a large quantity of chlorine into the pool, even in the evening, the next day there may be a high residual chlorine value and the sun will start rendering the chlorine harmless.
3. Keep your residual (free or available) chlorine levels between 1.0ppm to 3.0ppm.
4. Keep your pool pH at about 7.2 as that is a level where the chlorine is very effective and the water is comfortable on the swimmer’s eyes. At a pH of about 8.2, chlorine has lost about 90% of its effectiveness.