Pool Algaecide - What Does It Do? How Do I Use It?

Algaecides are a commonly-used pool product that both kills off algae and prevents new algae problems from developing.

These products contain specialised chemicals and other metallic compounds that are more effective at killing algae than your pool’s sanitiser alone.

In this article, we will discuss what pool algaecide is, when to use algaecide, and a variety of active ingredients you may find in these products. We also include information about how to use algaecides as a preventative measure or as an algae treatment for pools.

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What Is Pool Algaecide?

Pool algaecides are specialised chemicals that contain antimicrobial agents known to be effective on algae cells.

Algae cells are technically not classified as plants, animals, or bacteria (with the exception of blue-green algae), but actually belong in their own category, which is called protists.

Protists are microorganisms that dwell in moist or wet environments and share some similarities with plant cells.

This lends them a stiff outer wall which can give certain types of algae a resistance to chlorine. Algaecides typically contain agents that are meant to puncture the cell walls of the algae, allowing for them to be killed off more easily.

Unlike traditional sanitisers for your pool which have antibacterial and oxidising properties, algaecides are designed to have antiprotistal properties.

While it’s not necessary to learn all of the biological properties of algae cells, knowing that they are classified differently can help you better understand the algae treatment process.

When To Use Algaecide In Your Pool

Algaecides are designed for use as a preventative agent. Once added to your pool, these products can prevent algae from forming for a period of up to three months.

The compounds contained in algaecides are safe for swimmers, so one preventative dose is well worth the long-lasting effects.

Algaecides are not suitable as a first line of defence against active infestations or green pools, and are not primarily a pool algae killer. These products can be used in the algae treatment process, but are most effective once almost all of this algae has been killed off with shock treatments.

Using an algaecide on a pool with an active infestation is not as effective as shock treatments because algaecides do not contain oxidising agents. Oxidizers are the main components of your pool’s sanitiser, and these are capable of working much faster than algaecides.

Perform shock treatments as needed before adding algaecide products.

Using a shock treatment following the use of an algaecide is strongly discouraged because it can cause compounds in the algaecide to oxidise, making both your shock treatment and the algaecide less effective, often leading to pool stains.

Active Ingredients In Algaecides

Pool algaecides often contain copper. This metal is highly toxic to algae cells specifically and also has other antimicrobial properties.

Algaecides with copper may contain organocopper or chelated copper, which has been bonded with amino acids, making it less likely to interact with other compounds in the water. This can reduce certain side effects such as staining and foaming.

There are also copper-free formulas of algaecide. Most of these algaecides contain quaternary ammonium disinfectant compounds, sometimes referred to as ‘quats’ for short, and may also contain polymers.

One common quat used in pool algaecides is benzalkonium chloride. These agents have an oxidising effect like chlorine, but unlike chlorine, they are more stable around carbon and therefore still highly effective when other organic compounds are present.

How To Add Algaecide To Your Pool

Choose An Algaecide

When using an algaecide preventatively, we recommend using one that is effective on several types of algae, unless specific types of algae are common in your pool or area.

When choosing an algaecide as a step in the infestation treatment process, it is important to pick one that is known to be effective on the type of algae you are experiencing.

Most algaecides are effective on multiple strains of algae, but certain stubborn strains such as black spot and mustard algae benefit from using specialised algaecides.

Before shopping for an algaecide, determine the type of algae present in your pool based off of the colour, texture, and patterns that you observe.

If you have a pool with an ioniser, you should avoid algaecides that contain metal-derived compounds. You may also choose to use a metal-free algaecide if you have a high amount of dissolved metals in your pool’s water already, or if you frequently experience metal staining.

Prepare Your Pool’s Chemistry

Algaecides, whether they are used preventatively or as a treatment, should always be introduced to your pool after any sanitisers such as chlorine. Therefore, it is essential to balance your chlorine levels before adding these products.

If using a shock-treatment, wait until chlorine levels return to normal before adding your algaecide.

If you are adding algaecide preventatively, make sure your chlorine levels are balanced beforehand so that you will not have to add chlorine while the algaecide gets acclimated.

Before you start, it is also a good idea to make sure that your pool’s pH falls within the ideal range of 7.2-7.6, as many algaecide products (along with your pool’s sanitiser) are more effective at these levels.

Add The Algaecide To Your Pool

When preparing to add algaecide to your pool, take note of the dosing instructions on your product’s packaging to find the right amount of algaecide to add to your pool.

Some products may contain different dosing instructions for preventative use vs for the treatment of existing algae, so pay attention to these directions.

You may also wish to use our algaecide calculator to help you calculate an appropriate dose.

Distribute the dose of algaecide you have measured out around the perimeter of the pool while the pump is running.

Your pump should be left running for about 24 hours following the addition of an algaecide in order to get the product adequately circulated, so be sure to override your pump’s timer if you have one set up.

Algaecide can sometimes cause foaming upon being added to your pool (especially if you add too much). Although this is a normal occurrence and usually goes away on its own within a 24-hour period, some pool owners find this condition frustrating.

If you find algaecide foam to be a nuisance, check out our article on how to get rid of algaecide foam.

Companion Products

Phosphate removers make a great companion product for algaecides. These products work to remove phosphates, an organic molecule that algae cells feed on as they grow and reproduce.

By removing phosphates from your water, you can further decrease the chance of an algae problem developing.

Phosphate removers are available in a variety of strengths. To learn more about these products and how to choose the right one for your pool, check out our ultimate guide on phosphate removers.


Algaecides are a great product to use to prevent algae problems from developing in your pool.

If your pool has already developed an algae infestation, you may choose to use an algaecide in your treatment process, but only after thorough shock treatments have been performed to kill off as much active algae as possible.

Do you have any questions about using algaecides in your pool? Get in touch with us in the comment section, we would love to help!

Louis from Pool Advisor


A chemical engineer by trade, Louis is committed to debunking myths in the pool industry by explaining the underlying chemistry and making it accessible to all.