The water's pH is a measure of its total acid-alkalinity balance -- the relative proportion of acids and alkalis in the water. Simply put, water that is either too acidic or too alkaline will cause undesirable chemical reactions. If the water is too acidic, it will corrode metal equipment, cause etching on the surface materials and cause skin irritation. If the water is too alkaline, it can cause scaling on the pool surface and plumbing equipment and can cloud the water. Additionally, both high acidity and high alkalinity alters the effectiveness of the chlorine. The chlorine won't destroy pathogens as well if the water is too alkaline, and it will dissipate much more quickly if the water is too acidic. On the pH scale, zero indicates extreme acidity, 14 indicates extreme alkalinity and 7 indicates a neutral state. The recommended pH-range for a swimming pool is between 7.2 and 7.8. To raise or lower pH, acids or alkalis need to be added to the water. For example, adding sodium carbonate (soda ash) or sodium bicarbonate (baking soda) will generally raise the pH, and adding hydrochloric acid (approx. 30% solution) or sodium bisulphate will lower the pH. Maintaining the proper balance of chemicals in the pool is a continual process, because any new element (oils from a swimmer's body, a shot of chlorine, stuff that falls in the water) changes the chemical composition of the water. If the pH is too high, not enough pool cleaning can take much longer than normal. Once the chemicals that make up the chlorine have cleaned the pool water, their residuals either combine with another chemical, such as ammonia, or are broken down into single atoms which render the chlorine harmless. Sunlight speeds these processes up – that is why, particularly in warm climates like the Middle East, it is necessary to add chlorine to the pool more frequently than in other, cooler places. In addition to pH, the following levels should also be checked: total alkalinity, calcium hardness and total dissolved solids.
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 contained in chlorine can also cause many fabrics to fade quickly when not rinsed off immediately after exiting the pool.
There are other sanitizing systems available to disinfect the water in your pool. Although, many systems claim to be chlorine-free, many of them actually work in conjunction with chlorine to sanitize the pool. Effectively this means that the chlorine content in the water is reduced, thereby reducing the possible adverse side effects mentioned above. Many 'alternative' systems attempt to justify their purchase by touting a savings of "90% chlorine". Pool owners are even told to cut back on the pool chlorine level to prove this savings. Wrong!! Cutting back on the level of pool chlorine to save money is like using a credit card to conserve cash it works fine until the bill appears and the true cost becomes known. The same goes for reducing chlorine levels. The water may look fine for a while (how long depends on bather load) but when the filter cycle shortens and the water becomes turbid, a good chlorine shock will be required ... some great savings! The true test for chlorine savings is not by reducing FAC levels but by maintaining your standard levels to see if the alternative system being tested will maintain these levels with a 90% reduction of chlorine usage!