Ridding Your Pool of Black Algae

Any kind of algae growth in your pool is undesirable, but black algae is easily the most noticeable, unattractive, and stubborn variety of algae that is likely to invade your pool. As many pool owners are afflicted with a seemingly unconquerable black algae problem, it will be helpful to address the issue of how to best remove black algae from pool water and surfaces.

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What Causes Black Algae Grow in Pool?

The ultimate source of black algae is the ocean, and thus, the most common means of it getting into your pool is via swimming suits or other items that have touched ocean water and then touched your pool water. It is also possible for oceanic birds to carry black algae into your pool on their feet and feathers.

However it gets there, once it is in your pool, black algae develops some of the deepest roots of all algae species and attaches itself to your pool’s walls and floor. Its protective outer layers allow it to survive normal chlorine levels, and it particularly thrives in the shade.

Growth of black algae is encouraged by too-low chlorine levels, improper pH, alkalinity, and water hardness. Lack of sufficient water circulation is another factor that will increase black algae. Thus, the failure to perform normal pool care aggravates a black-algae problem once a pool has already been contaminated.


How Can I Get Rid of Black Algae?

When black algae are in your pool, removal can be a significant chore. First, you must eliminate the sources of black algae. Wash your swimming suits, pool toys, floats, and all pool equipment thoroughly with bleach.

Next, you will need to purchase some algaecide, preferably one that contains copper since these are the most effective. Pour the liquid all across the pool’s edges, using the amount prescribed by the manufacturer for your pool-size. Also, pour some directly over infected areas, and take a scrub brush to the algae spots. The roots are deep, so you may need to scrub several times to get it all off.

Finally, you will want to triple-shock your pool to finish the algae off. Use three pounds per 10,000 gallons instead of the usual one, and be sure to shock it at night. Run the filter for a full 24 hours or however long it takes to eliminate the black algae.

How Do I Prevent Black Algae From Returning?

To prevent a return, you should be careful to practice good pool maintenance. Keep the chlorine, pH, hardness, etc. consistently at optimal levels. Run your filter at least 8 to 12 hours every day. Shock your pool about once a week. Vacuum and scrub your pool as needed throughout the swimming season.

The second practice that will keep black algae down is to use “preventative medicine” such as Algi Bloc by Magic Pools, which will continually fight against its growth all year long. You can even use it in your winter pool formula to keep down black algae for as long as six months.

Finally, simply using different swim attire and accessories for ocean swimming versus for pool swimming will help prevent resurgence. Alternatively, you can simply wash, dry, and bleach all swimwear that has been used in the ocean before using it in the pool.


If you are dealing with black algae in pool removal can be accomplished with algaecides and intense cleaning. Prevention can be accomplished with similar products, regular pool maintenance, and segregation of pool and beach swimwear. With only a little knowledge and effort, black algae pool problems can be eliminated.

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