How to kill pool algae with bleach

Updated April 17, 2017

Bleach is a cheaper way to kill algae in a pool than branded pool chemicals. The active ingredient in household bleach is chlorine, the same main ingredient found in pool products designed to chlorinate a pool. However, to use bleach safely in your pool you need to follow some simple guidelines. Chlorine is a popular disinfectant that also kills algae. The chlorine found in household bleach is made up of sodium hypochlorite and water. Before you use bleach to treat your pool, you may also want to consider the environmental impact of it. Chlorine in water creates trihalomethanes (THMs). According to Environmental Controls & Methods Inc., THMs are in the top 10 carcinogens that affect humans.

Test the pool's pH level. The ideal pH level in a pool is 7.4 to 7.6. When your pool's water is in the ideal pH range any bleach that you add to it will work better.

Scrub the walls of the pool. Take a pool brush and brush the walls of the pool that are affected by algae. This makes it easier and quicker to kill the algae.

Add bleach to the pool. Household bleach has a much lower concentration of chlorine than pool treatments. Bleach that you buy in the supermarket is normally 5 per cent chlorine, while pool chemicals start at 12 per cent chlorine and can rise up to 95 per cent, according to the United States Environmental Protection Agency. For every 10,000 gallons of water in your pool, add 1 gallon of bleach. Use plain unscented bleach that does not have any extra uses listed on the label, such as whitening. Use gloves while handling the bleach, as spillage could irritate your skin.

Turn on the pool filter. The pool filter will need to run continuously for 24 hours when you are treating water with an algae problem. During this period you will also need to empty the filters a number of times. When the algae is dead it will turn a greyish colour and there will be no green left. If there is still green algae in the pool, it may need another dose of bleach and filtering. The dead algae will often make the pool cloudy. At this stage you should vacuum the pool and also backwash the pool filter.

Test the pool's water with a pool test kit. When the algae problem has been dealt with use a pool test kit to ensure that the chemicals in the pool are safe for swimming. The National Institute of Technology, Tiruchirappali states that the levels in the pool should be as follows: free chlorine 2.0 to 4.0 parts per million, pH 7.4 to 7.6, total alkalinity 80 to 100, calcium hardness 200 to 400, and cyanuric acid 30 to 50 parts per million. If the levels are not in the correct range add the appropriate balancers to the pool. The pool is safe for swimming when the levels are balanced.


The free chlorine in a pool should never fall below 1.0 parts per million.

Things You'll Need

  • Plain household bleach
  • Pool test kit
  • Pool vacuum
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About the Author

Siobhan Russell has been freelance writing for the Internet since 2003. She has written articles covering a variety of subjects for Travelwand, Yellow Pages and eHow. Siobhan has a particular interest in writing travel and equestrian articles. She has a BA Honors in History and Philosophy from National University Ireland, Maynooth.