Algae growing in a swimming pool is a perenial problem for the swimming pool owner here we will examine the 4 most popular ways to get rid of it. These are

  1. Chlorine
  2. Copper
  3. Quats and Poly Quats
  4. Phosphate removal.

As we will see some of the above can be used to kill algae and some are only useful to prevent it forming in the first place. Algae can be introduced to the pool by rain, falling leaves, wind or even bathing suits transfering algae from one body of water to another. Planktonic clean water algae float on the surface of pool water while other types will attach and grow onto the pool floor or sides.  Many factors affect the development and growth rate of algae. Water temperature, sunlight, pH, mineral content and lack of chlorine residual of the pool water will all help to encouage algae development.


Chlorine gets a bad press but since it was discovered that chlorine kills germs its use as a sanitiser in drinking water has saved millions of lives worldwide. Chlorine is the only chemical that acually kills algae. It acts in the same way as setting fire to the algae, it oxidises it.  When you have a bloom of green algae in your pool then by far the best thing to do it to blast it with a shock dose of unstabilised chlorine. What is not used up in killing the algae will be burnt off by the sunlight.


Copper does not kill algae it disrupts its metabolism and stops it reproducing. Copper can be introduced in to the water in two main ways as a chemical or by an ionizer. Too much copper can cause stains on concrete pools so chemicals that contain copper also contain a chelating agent, a stabiliser, that does not allow too much copper in to the water at any one time.

Quats and Poly Quats.

Quat is the short hand term for a family of chemicals called quaternary ammonium compounds.  Again they do not kill algae they disrupts its metabolism. Quats are short lived and you need to keep adding them to the water to keep algae at bay. They are a cheap chemical but they affect the surface tension of the water and cause it foam, foaming is perfectly normal but many pool users don’t like it. A high level of Quat will kill off an algae bloom but even so chlorine is still better for this so quats are usually used at lower levels as a preventative. Poly Quats or polymeric quaternary ammonium compounds are long chains of Quats and although they are more expensive they last longer and don’t cause foaming of the water. These are marketed as Long Life Algicides and are the popular form of Algicide in liquid form.

Phosphate Removers

All of the above chemicals act by meeting the algae head on and killing it. Phosphate removers act in a more subtle way. Algae must have phosphates present to be able to grow. Remove phosphates from the water and the algae are starved to death. Compounds of Lanthanum are used to react with the phosphate and precipitate it out where it is picked out by the filter.

All of the above methods are good at killing or preventing algae and you can mix and match any of them or even use all four methods.

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