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What is Algaecide?

By Jane Harmon
Updated May 16, 2024
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Algaecide is a chemical treatment for swimming pools, fish ponds, and other water features that kills algae, very small organisms that grow in water or very damp environments. Algae in pools and ponds can cause the water to become cloudy and, in some cases, can form a scum over the surface that blocks sunlight from the water. It is the cause of the peculiar "red tide" phenomenon, in which the ocean appears to be covered in blood. Usually, their presence unsightly, but it can also be dangerous — certain kinds of algae give off toxins that can be hazardous to humans, fish, and plants.

A commercial algaecide is a quick and easy way to remove algae from your pool or pond. When it's used in a swimming pool, it allows the owner to use less chlorine for water purification, resulting in water than is more pleasant to swim in, without the stinging eyes and nose that too much chlorine can cause. Regular use also prolongs the life of the water filtration system, as there is less plant material to clog the filters and intakes of the pump.

Consumers should select a product based on what it will be used for. Some aren't suitable for use in water that contains living fish, for example, so homeowners should read the label and follow the directions closely. Even too much of an algaecide intended for ponds can be harmful to the fish, and change the pH levels of the water too much. This chemical can be purchased online, but shoppers who have questions might be better off visiting a local nursery that supplies water feature materials or a pool cleaning supplier.

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Discussion Comments
By wavy58 — On Jul 27, 2011

Mustard algae conquered my swimming pool one summer. It was so small that it could pass through the sand filter, and it resisted normal chlorine levels.

My pool specialist told me to first brush it with a stiff brush. Then, I had to backwash it while vacuuming to flush it out. I adjusted the pH level and added extra chlorine to prevent re-infestation.

Then, I turned off my pump and treated the spots with algaecide. I left it on there overnight. Then, I turned the filter back on and backwashed while vacuuming once more. Finally, I got rid of the stuff.

By kylee07drg — On Jul 27, 2011

Swimming pool algaecide is not cheap. If you wait until you have the problem, you will pay at least $14 for a regular sized bottle of the stuff.

Prevention is the best method. You can buy 20% algaecide to prevent the stuff from ever forming. Also, you can buy bags of shock that have algaecide in them. Since you are supposed to shock your pool once a week anyway, you get the added bonus of algae treatment.

Whatever you do, don’t wait to treat the problem. It is best to address it as soon as you notice it, because if you wait, you can grow new kinds of algae that are tougher and more expensive to get rid of. You may end up needing to consult a pool specialist.

By shell4life — On Jul 26, 2011

I use algaecide to kill green algae whenever my pool starts to feel slick or takes on a greenish hue. One full 14 ounce bottle usually takes care of the problem in my four-foot deep pool.

I use the 50% algaecide solution. I pour it slowly into the water in front of the jet so that it gets sent shooting into the pool. I leave the pump on to circulate the algaecide throughout the water.

After three days, the algaecide has killed all that it is going to kill. Then, I can vacuum the dead algae off the bottom of the pool and backwash it.

By Oceana — On Jul 25, 2011

I had the strangest algae I had ever seen develop in my above-ground, 24-foot pool this year. It was pink and stringy, and it kind of reminded me of insulation. It got all caught up in the skimmer, and it hugged the edges of the pool liner.

I took a pool water sample to the pool store, and the guy there gave me something that is supposed to kill yellow algae. He said it should knock the pink out as well. I certainly hope it does, because I’m scared about what it might do to my health!

By GardenTurtle — On Jul 25, 2010

There are actually different groups of algaecides. Quats, polyquats, copper salts, and colloidal silver are the most common.

Quats are the best selling and lowest priced algaecides. It is often used as a preventive measure instead of for existing algae.

Polyquats are more costly than quats but are very effective. It is not only useful on green algae but also with mustard and black algae.

Copper salts are quite effective and is used mainly in ponds and lagoons. It can be used in pools but it can cause stains. Over time, the copper salts can deposit on pool walls leaving a bluish look.

Colloidal silver is similar to copper. It attaches itself to the floor and walls of the pool giving a continuing algaecidal action. It, however, can also cause staining.

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