Correctly balancing the chemicals is one of the hardest tasks for any pool owner. Pool chemicals are harsh and toxic, yet are absolutely essential. Pool chemicals perform a variety of functions, including controlling the growth of bacteria and other organisms, maintaining a safe balance of acidity versus alkalinity (known as pH) and adjusting the relative hardness of the pool water. When the chemicals are properly balanced, the pool is clean and safe for swimmers.

Water pH

The pH of the pool water should be tested weekly. A low pH indicates that the water is too acidic. The pool surfaces can be etched and damaged, creating pockets for algae to flourish. Swimming is uncomfortable and even dangerous, as the acidic water dries out skin and irritates eyes. A high pH, indicating alkalinity, is equally dangerous. Scale deposits of calcium carbonate can form, causing buildup on the pool's walls. The pool's sand filter can clog. High alkalinity can dry out skin and irritate eyes and noses. The ideal pH for swimming pool water falls between 7.0 and 7.6. Perfect pH is considered 7.2, the natural pH of human eyes. To adjust the pH level, use an acid in an alkaline pool or an alkali in an acidic pool. The most common pool acid is muriatic acid. Protect your eyes, skin and clothes when handling muriatic acid, which can cause severe burns. Common pool alkalis are baking soda and soda ash.

Chlorine

Chlorine acts as a disinfectant in the pool. Too little chlorine allows bacteria to grow and waterborne illnesses to spread. Too much chlorine is caustic, causing irritation and skin problems. Test the chlorine level at least once a week, or twice in extremely hot weather. The ideal level of chlorine in a swimming pool is 1.0 to 3.0 parts per million. If the chlorine level is low, add chlorine according to the manufacturer's instructions. The chemical is toxic, so protect your eyes, skin and clothing.

Pool Shock

If your pool water is green, if you have a buildup of algae or if the pool smells strongly of chlorine, the pool may need to be shocked. Pool shock is a highly concentrated form of chlorine that rapidly raises the chlorine level as high as 10.0 parts per million. Shock the pool in the evening to allow at least eight hours before swimming. Always test the chlorine level before re-entering the pool.

Less Common Chemicals

Once a month, test your pool water for total alkalinity, calcium hardness and stabilizer. If you maintain your pool regularly and your water is not overly hard, these levels are generally acceptable. If they are out of range, various chemicals can be used to adjust these levels, but it is best to seek the advice of a professional.

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Pool Water Testing

For example, it's your first time adding water on your pool. First add your metal preventer that is in your area to prevent staining. The next step is to adjust your alkalinity to between 80-120 ppm. And lastly, is to adjust your PH to 7.2-7.5 24 hours. After this is done, you can now add your Chlorine from 1.0 to 5.0 ppm. 3.0 is ideal in a pool. Source: http://www.cheappoolproducts.com/1_0_0_Pool~Chemicals_83~supplies.html