Understanding Pool Algaecide – What Is It?

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You might know how it feels to gaze outside at your pool and have an off-putting green coating dampen your moment of pride. Algae is ugly and often unhealthy, releasing toxins into pool water that can cause harm to people and pets.

Controlling algae isn’t difficult, and that’s where pool algaecide comes into play. Pool algaecide is an important tool to have in your pool-care arsenal, but many pool owners aren’t fully aware of this chemical and the role that it can play in maintaining pool safety and cleanliness. 

Let’s break down the essentials of pool algaecide and how it combats nasty layers of algae that damage equipment, our health, and the environment.

Where Does Pool Algae Come From

Algae consist of aquatic organisms that group together under specific circumstances in stagnant water. Algae easily reproduce and spread, wreaking havoc on expensive pool systems. 

The most common type of algae in pools is cyanobacteria algae. It’s almost always green or blue and can make people and animals very sick if they come into contact with it.

The Elements

Cyanobacteria spores travel through the wind. Part of its commonality comes from the fact that the wind carries and distributes its particles swiftly and over a great distance. Rainwater can also introduce algae spores into pools. 

Latching On

The other factor is how easily it transfers from one body of water to another by sticking to swimwear. For someone who swims in the ocean and then wears that same swimsuit into a pool without first thoroughly cleaning the garment, there’s a high chance that algae spores are coming with it.

The same thing goes for any pool or beach toys, floats, or other kinds of equipment that move between bodies of water without proper cleaning. Algae latch to these items and reproduce once they come into contact with new water. 

Poor Circulation and Filtration

One of the fundamental conditions for algae growth is stagnant or slow-moving water. Pools have circulation systems that constantly keep the water moving, but any dead spaces can promote algae development. 

Most commonly, pools with weak or faulty filtration systems experience more algae growth because the water circulation and filtration aren’t strong enough. Large pools using too small filters suffer dead and low flow areas that manifest algae.

Bad pH Balance

Pool owners need to regularly test water levels to determine the calcium, alkalinity, pH, and cyanuric values. The appropriate balance of these minerals combats algae production and even a slight offset has the opposite effect. 

Insufficient Chlorine

Universally, we chlorinate pools for sanitation. If there isn’t enough chlorine present, the hypochlorous acid that kills sinister germs will be unable to fight off algae-inducing bacteria. 

High Water Temperature 

Pool water that is too warm, either from electronic heating systems or natural warmth occurring from exposure to sunlight, fosters algae. Warm water depletes chlorine levels, heightens evaporation, and throws off the pH balance. 

How Algae Causes Harm

Pool algae threaten equipment and pose health hazards to humans and animals. Preventing and managing algae blooms is a critical responsibility for pool owners.

Pool Algae Health Risks 

Coming into contact with algae can cause skin infections that present as horribly itchy rashes or skin breaks that make people vulnerable to more severe infections

If the eyes come into contact with algae, they can easily pick up infections like conjunctivitis, which people commonly refer to as “pink eye.” Ear infections are also frequent for swimmers who come into contact with algae.

Accidentally ingesting algae in a pool can bring about dangerous fevers and diarrhea. It also opens someone up to a host of bacterial infections, as algae harbor dangerous bacteria like e. Coli.

Algae is also notoriously slippery, and swimmers can experience physical injuries like cuts, scrapes, bruises, and broken bones from accidental falls. Suffering a cut or scrape in algae-infested water heightens the risk of picking up a serious infection.

The same toxins and bacteria that put people at risk cause harm to pets too. Do not let your pets swim in an algae-infested pool, and if they do get in the water, rinse them off thoroughly, and don’t allow them to lick their fur until they are properly clean.

Aside from these risks, algae cause low visibility, which can hamper rescue attempts if someone struggles to swim below the surface or falls unconscious while swimming.

How Algae Hurts Pools

Algae is a threat to people and pool equipment alike. Algae strands clog sanitation pathways and filters, damaging the system. It can also stain the pool surface, and severe infestations threaten structural integrity.

Pool Algaecide Types

Now that we’ve examined how and why pool algae will manifest, let’s take a closer look at the various types of algaecide and how it serves as a powerful eliminator and prevention of pool algae. 

Algaecide is a mix of chemical additives with different active ingredients that kill and prevent algae. The type of chemical compound that you should use depends on the type of algae that is present. 


The first algaecide type is one with copper ions as the active ingredient. This algaecide compound usually contains copper sulfate. People use it widely because of its effectiveness in controlling algae growth, but it commonly causes pool staining during the process.

Copper-based algaecides also aren’t environmentally-friendly, but they work well for spot treatments across large pools.


Ammonium-based algaecides consist of organic materials that use nitrogen to discompose algae cells at the membrane. This algaecide variety is eco-friendly but only effective against typical green algae. 

The general complaint about this algaecide is the foaming that results from treatments. 


Polyquat compounds also don’t carry negative environmental side effects without sacrificing power. These algaecides are incredibly effective against algae formations, including green, yellow, and black algae. 

Plaster pools attract stubborn black algae, and yellow algae are famously chlorine-resistant. Poly algaecides have the force these more difficult algae require, but it’s important to keep in mind that algaecide is much more effective as a preventative measure.

Poly-electrolytes are stronger than the components of ammonium-based algaecides and eliminate the foaming effect. Note that the potency of this compound calls for precise dosages and application. This algaecide variety also retails at a higher cost. 

When and How to Use Algaecide 

You should break out the algaecide at the first notice of murkiness and abnormal coloring in your pool water. Pool cleaning professionals recommend administering a shock treatment and waiting 24 hours for the chlorine levels to return to normalcy before adding algaecide.

Another appropriate time to do an algaecide treatment is annual, before closing up the pool for winter months. 

Before you add the chemicals, test the water levels for the pH and chlorine values. You need to read and follow the product instructions carefully, as each algaecide has specific directions.

Add the algaecide around the perimeter edges of the pool to best ensure equal distribution of the chemical compound throughout the body of water. Keep the pool pump running as you mix in the additive to help it circulate.

Once the algaecide is in, allow the pool filter to run for a full 24 hours to circulate the water and help remove dead algae. You also need to brush the floor and walls of the pool with a nylon pool brush to loosen algae that cling to those surfaces, making it easier for the chemicals to kill.

How Much Do I Use?

The three considerations for the algaecide amount you’ll use for treatment are how much algae is present, how large the pool is, and which type of algae you’re working against.

A dependable guideline for determining dosage is matching 1 PPM (standing for part-per-million) of the chemical compound for every 10,000 gallons of water you’re adding it to. 

If you have a 10,000-gallon pool you would add 1 PPM, if you have a 20,000-gallon pool you would add 2 PPM, and so forth.

This is still just a guideline, and it’s always best to consult the instructions that pair with the specific algaecide you’re using. Each variety has different elements that can impact the dosage. For example, a higher concentration might require adding less of the algaecide.

Adding too much algaecide can damage your filters and irritate swimmers’ skin and eyes the next time they use the pool. 

Other Areas Algaecide Helps

In addition to eliminating and preventing pool algae, pool algaecides combat other molds and bacteria. 

Pink Slime

Pink slime resembles algae, but it’s an airborne bacteria. This pink and orange coating grows in pools’ dark crevices and sometimes sticks to ladders and light fixtures. It can expand its coverage to the entire pool area if left untreated. 

Similar to algae, pink slime enters the human body through the eyes, ears, mouth, and scrapes or cuts. It causes lower respiratory tract infections, urinary tract infections, and illnesses like pneumonia. 

Pink slime attributes pool presence to poor pool cleanliness or chemical water imbalance. Pool algaecide treatments help to ward off unattractive and dangerous pink slime.

To use algaecide for pink slime control, start by cleaning the pool filter and balancing the pool water’s pH levels. Turn off the pump before brushing the pool’s floor and walls with a nylon brush and then add the algaecide. 

There are algaecides available that specifically treat pink slime, but you’ll have to use the correct product depending on whether your pool is chlorinated or biguanide. 

Shock the pool or add an oxidizer and allow it to rest overnight with the pump off. Biguanide pools require quadruple the shock amount that chlorine pools do, so make sure to assess your pool’s needs before acting.

White-Water Mold

White-water mold is a common fungal growth that occurs on pool water surfaces. Like pink slime, a pool that lacks proper sanitation or off-kilter chlorine chemistry fosters white-water mold.

White-water mold is unsightly but isn’t a health hazard on its own. It can clog filters like algae, and improper filtration can cause a pool to harbor bacteria and toxins. 

Pool algaecide’s chemical compound sanitizes and oxidizes pool water to prevent white-water mold from growing.

Treating white-water mold with algaecide is a similar process to treating pink slime. You need to clean the pool filter and balance the water before shocking the pool. The pH value should fall between 7.4 and 7.6 when testing before treatments.

Brush the pool floor and walls before running the pump overnight and brushing a second time the next day. Afterward, vacuum the pool and clean its filter again. Test the water levels at the end to ensure everything is in proper balance.

Add algaecide after seven days to prevent new fungal growth.

Can I Swim After Using Algaecide?

Algaecide is safe for pools and swimming. Wait 30 minutes to one hour after using algaecide before swimming, but after that, it shouldn’t cause any irritation. 

Use algaecide as its instructions state and you can be confident that it won’t pose any threat to your pool or family. 

Final Thoughts

Pool algae are toxic, from health and equipment perspectives. Pool algaecide is a safe and powerful chemical tool for preventing and eliminating dangerous algae blooms in your pool water. 

Select the algaecide variety that matches the severity and identity of your pool’s infestation. Follow the product instructions closely and utilize algaecide’s sanitizing and oxidizing properties to keep your swimming pool beautiful, clean, and healthy.

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