How do I prevent algae in my pool?


Without proper chemical care, algae spores, which enter the pool water from the air, will multiply and become visible colonies. These colonies can take several forms and are identified by their colors. Of the many species of algae, only four are common in household swimming pools: green, yellow, pink and black.


Green Algae

Green algae is by far the most common type of fresh water algae. It can grow both on the pool surface, resembling a green, slimy stain, and also suspended in the pool water, causing the water to appear to have a green tint. In severe cases, the algae is concentrated enough so that it is impossible to see the pool bottom, or even the steps. This can occur without significant warning during the summer months and may even happen within a 24-hour period. For this reason, it is always advisable to make certain that the chlorine concentration is well within the ideal range.

Yellow Algae

Yellow algae (also called mustard algae) is actually a type of green algae, but because of its different appearance and somewhat more difficult removal procedure, it is discussed separately here. Yellow algae almost always forms on the pool surface, usually in shaded areas. It is yellow-brown in color, has a slimy texture, and can most often be brushed away with a few vigorous strokes of a standard pool brush.

Pink Algae

Pink algae is a relatively uncommon type of algae that is ink or red in color, and usually form around pipefittings and light fixtures on the pool surface.

Black Algae

Black algae is a very common type of algae, and is the most difficult to remove once it has formed, A colony of black algae always forms on the pool surface, and usually is first visible when it is about the size of a small fingernail, but can grow rapidly and eventually become larger than a dinner plate. The spores settle in porous surfaces, such as rough plaster (mostly caused by calcium buildup), and begins to anchor itself to the surface. It is able to dig a root into the porous surface and from there can develop an extensive root network beneath the pool surface, usually between the plaster and the concrete. Once the roothas been formed, the algae become visible, but at this time it is already too late. Destruction of the visible portion is by no means a guarantee that the entire. colony is destroyed.


The proper maintenance of pool chemicals is the best way to ensure the prevention of most types of algae. Some green algae, and virtually all yellow algae are immune to chlorine, so in these cases it is almost impossible to guarantee the prevention of all algae. However, there are algaecides available to the consumer, which use both chlorine and copper to collectively destroy these chlorine-immune algae. Black algae can most easily be prevented by ensuring that the pool surface is as smooth as possible. Maintaining a proper water hardness level, and ensuring that any damage to the pool surface is repaired as soon as possible are the best ways of keeping a smooth pool surface.


Once algae has become visible to the naked eye, it will require a great deal more time and expense to kill it than it would have to have prevented its formation. For this reason, the prevention of algae is stressed. With the exception of black algae, the destruction of algae means the total eradication of the colony from the swimming pool, and the pool is to be maintained as usual from that point on. With black algae, as mentioned above, the visible portion may have been removed, but a root still exists until at least a liquid chlorine bath can be performed, requiring the pool to be drained and scrubbed with liquid chlorine.

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