an introduction to algicides...or algaecides

Before we break down all the different pool algaecide (or algicides) first let’s tackle what makes an algicide…well…an algicide.

Sodium Bromide Based Algaecides

We’ll start with our favorite type of algicide: sodium bromide based. We introduced Sodium Bromide based algicides to the pool industry in the early 1980’s with Yellow Treat.

The sodium bromide component remained a secret until the 1990’s. Then EPA required us to disclose it on the label, leading to companies launching their own Sodium bromide based algicides.

How it Works

When sodium bromide reacts to chlorine in water, it replaces active chlorine (hypochlorous acid) with active bromine (hypobromous acid). Active bromine is much stronger and at higher concentrations across the pH range of the pool when compared to active chlorine.

There are other temporary reactions as well. Such as forming BromoChloride which is an extremely powerful oxidizer. This “burns” the algae out of the water.


Generic (99%)

Most sodium bromide based algaecide sold in the pool industry is a generic salt repackaged. Sodium bromide is produced as a salt in concentrations of anywhere between 97-99% purity. This is sourced from abroad and shipped over to the manufacturer where it is packaged in a bottle for sale. Two 99% sodium bromide products will be exactly the same. Any price difference is really just packaging and marketing.

Formulated (United Chemical)

While our pool algaecide contain Sodium Bromide, we mix it with other ingredients. The other ingredients change how the Sodium Bromide reacts, making it stronger, improving the reaction, and stabilizing the chlorine reading.

benefits vs drawbacks

Ammonia-based algicide

Ammonia based algaecides specifically contain Ammonium Sulfate as their active ingredient.

How it Works

Mixing ammonia and bleach directly is extremely dangerous. When you add them separately into a pool you get a kick that kills algae.

Depending on the amount of chlorine and ammonia that is mixed, you get several different reactions. One of these is the temporary release of pure chlorine gas, which gives shocking your pool an extra kick. The ammonia compounds can also bind iron in algae cells, which can help kill them.

After that, the chlorine reacts to form chloramines, also referred to as combined chlorine. While they have some algicidal properties, they also contribute to eye burn and that “chlorine” smell. To break up the chloramines means shocking the pool again without adding any more ammonia. This makes Ammonia based algaecides a two-shock treatment.

benefits vs drawbacks

Quat Algicide

Quats or quaternary compounds are a very popular algicide. And they too contain ammonia compounds. However, they work a little differently than regular ammonia sulfate.

How it Works

Quaternary compounds kill algae by messing with the cell wall. This causes some of the interior cell to “bleed out” and thus die. This means that quats don’t require shocking.

However, as the compound breaks down and reacts to chlorine, it can still form chloramines that require shocking.

Also worth mentioning is that all quats in the pool industry are made by a single manufacturer and simply repackaged. So like 99% Sodium Bromide, the difference in price is just packaging and marketing.



Monoquats, sometimes just referred to as “Quats” are cheaper than Polyquats. However, they are much less effective at killing algae and tend to foam.


Polyquats are more expensive. However they are much stronger than monoquats, and don’t foam.

benefits vs drawbacks

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No Staining

Quat algicide has zero risk of leaving stains.


Metal-based algicide

Metal might be the first algaecide ever used. Metal’s algicidal benefits have been known since ancient times.

How it Works

Specific metals, like copper and silver, in high enough concentration will “poison” algae. It is believed that the metal ions disrupt certain processes in the cell to lead to death.



Ever wondered why a wishing fountain never gets algae? Because of the copper in the pennies. This is the same reason many civilizations used copper water vessels. Copper-based algaecides are extremely effective at hindering algae, and is the most common type of metal based algicides.

However, eventually that copper has to go somewhere. In the case of pools, this leads to blue-green stains on the surface.


Silver is stronger than copper at killing algae. It’s also considerably more expensive. Usually silver is reserved for the toughest to kill algae, such as Black Algae.

Like copper, however, it is also prone to staining. Silver will often leave grey to black stains on the surface.

benefits vs drawbacks