Optimal Level

• According to California Environmental Management, swimming pools should have a free residual level of 1.0 parts per million, or 1.5 parts per million if you use cyanuric acid (a chlorine preservative). Free chlorine residual level is the measurement of residual chlorine in the water as chlorine gas, hypochlorous acid, and hypochlorite ion. During certain treatments, such as a shocking treatment, chlorine levels can go as high as 10 parts per million to 30 parts per million, making swimming off limits. Swimming can resume 8 to 36 hours after shock treatment when chlorine levels measure between 1 to 3 parts per million.
  
  

Water Testing

• You should monitor chlorine levels daily using a water testing kit. If using cyanuric acid, measure monthly. Other test values, such as total dissolved solids, alkalinity, and water and calcium hardness, should be measured to maintain water quality. These values can be measured less frequently than chlorine.
  
  

Reducing Increased Levels

• Chlorine should never measure more than 5.0 parts per million in a pool. High levels usually occur from adding too much chlorine or after an intense chlorine shock treatment. Levels of 1 to 3 parts per million are considered safe, although 1 to 1.5 parts per million is ideal. You can use an agent called sodium thiosulfate to reduce chlorine levels that measure too high.
  
  

Chlorine Shock

• Chlorine shock is the removal of excess combined chlorine. Combined chlorine is composed of bacteria and chlorine that has merged as the chlorine killed contaminants. This chlorine waste is called chloramine. Shocking the pool raises chlorine levels for a short period of time to eliminate traces of chloramine and other waste.
  
  

Maintaining Chlorine Levels

• You can use an automated chlorinator to maintain a safe level of chlorine. This filtration houses chlorine tablets and processes the water with the tablets back into the pool. Maintain your chlorine levels by testing daily and adding chlorine when your testing kit indicates that your level is low. If you have a saltwater pool that uses a chlorine sodium compound, add the salt compound. If you have a traditional chlorine pool, use a chlorine floating dispenser.