Green Water

• By far, the culprit in the vast majority of swimming pool green water occurrences is green algae. Unfortunately, this microscopic green-colored plant can thrive in swimming pool water that has been poorly disinfected. In addition, a swimming pool that suffers from lackadaisical maintenance often will end up contaminated by algae. While algae themselves aren't disease-causing, their waste products can enable the growth of bacteria in a swimming pool, which can be potentially harmful to swimmers.
  
  

Disinfectant Levels

• Most often, a lack of adequate swimming pool water disinfectant leads to pool algae contamination. Whether a pool is chlorinated or brominated, to name two types of disinfectant, always make sure recommended levels are maintained. For chlorine pools, 2 parts per million (ppm) of free available chlorine are needed. In bromine pools 2 to 4 ppm of active bromine are required. Ideally, swimming pool bromine levels should be at 4 ppm.
  
  

Filtration Issues

• Along with inadequate disinfectant levels, insufficient pool filtration times often can lead to issues with green water from algae contamination. The algae can multiply rapidly. In many cases, a large green algae bloom literally will form overnight. Swimming pool filters should be operated at least 6 to 8 hours per day, with 12 hours being the ideal run time to maintain.
  
  

Eliminating Algae

• If your pool has green water from algae contamination, some work will be needed to clean it. The first step is to apply a strong algaecide, which should work to destroy algae. Next, brush and scrub the pool sides, walls and floors, and then vacuum the pool. After cleaning, your pool will require shocking, which means raising chlorine levels to at least 10 ppm. Chlorine should be stable at 2 ppm before swimming.
  
  

Considerations

• It may be necessary to repeat pool algae decontamination procedures at least one more time to eliminate algae completely. During the process, run your pool's filter continuously and backwash it (reverse the water flow through the filter) at least once. Lastly, make sure you restore your pool's pH level to between 7 and 8. Pool disinfectants work much better when pH is balanced properly. Also, soda ash can be used to raise pH and muriatic acid (MA) to lower it.