Chlorine

• Chlorine is the chief agent that keeps pools clean. Without the action provided by chlorine, pool water gets cloudy and infested with microbes. The chlorine in water disintegrates the chemical buildup of most microbes and doesn't allow them to live in the pool. Test the chlorine levels in your pool frequently. You must keep about three parts per million of chlorine in your pool.
  
  

Total Alkalinity and High pH

• If your pool's alkalinity and pH rise to a certain level, chlorine doesn't have as much of an effect on water as it should, leaving the water vulnerable to contamination. Much like the chlorine in your pool, you must also be aware of how much alkalinity you have and the pH of your pool. Always keep the pH within a range of 7.2 and 7.6 and alkalinity below 200 parts per million.
  
  

Shocking the Pool

• Once in a while, you need to add a large amount of chlorine into your pool to get its cleansing process back in order. This is a process known as "shocking" your pool. In this process, you add more chlorine than you normally would to the pool's water supply, effectively exterminating any microbes in it.
  
  

Lowering pH Levels

• Without a low pH, chlorine doesn't take action and keep your pool clean. To lower the pH, you must add an adequate proportion of sodium bisulphate (dry acid). This kind of substance acidizes the water and balances it off. Add the sodium bisulphate into the water in small amounts and keep checking the water's pH level after a few hours, repeating this process until the water reaches around a target pH of 7.2.