How To Clean A Swimming Pool That That Is Overgrown With Green Algae

If you have a residential swimming pool that has been inundated by stormwater or wastewater or has been neglected and is green with algae, it will be necessary to clean your pool manually. Merely adding chlorine will not be able to clean a pool that is overgrown with green algae. Here are the steps to take to thoroughly clean a swimming pool that is green with algae:   

  • Brush Algae From Sides of the Pool - With a coarse brush on a long handle, brush all visible algae off the sides of the swimming pool. Scrape all surfaces from the top edge down to the bottom of the pool to loosen as much algae as possible. Scrape the algae off and allow it to float on the surface of the water and then sink to the bottom of the pool.    
  • Clean Pool Filters and Pump - Turn off the pool pump and open the pool filter reservoir. Remove the pool filters and thoroughly clean them under running water to remove all debris and algae. Clean the skimmer basket as well. Remove the top of the pool pump and lift out the filter basket. Empty and clean the filter basket under running water to get rid of any debris. After cleaning, return the pool basket to the top of the pump, turn on the pump, and let it run continually for 24 hours before proceeding with the next step. 
  • Add Liquid Algaecide - After 24 hours, walk around the perimeter of the pool and pour one entire bottle of the liquid copper-based algaecide into the pool water. Because the pool filter is running, the algaecide will readily mix with the pool water. This additive can kill all of the algae and leave only dead organic debris. 
  • Add Pool Flocculant - Add a bottle of pool flocculant to the pool water while walking around the perimeter of the pool to make sure the flocculant is distributed evenly in all parts of the pool. This additive will cause the dead algae to clump together and sink to the bottom of the pool. 
  • Add Chlorine to the Pool Water - Add pool chlorine to the pool water in the usual proportions for your particular swimming pool. Use only pure chlorine (sodium hypochlorite or calcium hypochlorite) without any other additives. After a few hours, you can see the water begin to clear as the algae sinks to the bottom of the pool. Wait another 24 hours before proceeding with the next step. 
  • Skim and Vacuum the Pool - Use a pool skimmer to collect any large pieces of debris from the bottom of the pool. Next, use a pool vacuum to gather all the remaining dead algae and debris on the bottom of the pool. Start from the shallow end of the pool and vacuum down into the deep end. Depending on the volume of algae you had in your pool, you may need to vacuum the pool again and empty the vacuum reservoir more than once. 
  • Clean Pool Filters, Pump, and Basket - Once again, clean the pool filters, skimmer basket, and pool pump of the dead algae and debris from the last 24 hours. 
  • Test the Chlorine Level and PH Level in the Pool - Test the chlorine level and acidity level in the pool as you usually do for regular pool maintenance. If the chlorine level is low and the acidity level is high, adjust as needed by adding sodium bisulfate (dry acid) and/or muriatic acid.

After the above procedure, your pool should be clean, clear, and blue. If the water in your pool is still cloudy, you may need to repeat this process again to thoroughly clean it. Once you have destroyed all the green algae and vacuumed it out of the pool, you can return to a regular maintenance routine and schedule. It is a good idea to use an algaecide once a month (in proportions specified on the bottle) to make sure that all algae has been killed and does not return. With regular maintenance, you can have a blue swimming pool for your family and guests to enjoy.  If you don't feel comfortable cleaning your own pool, visit for more information.