ALGAE in Pool

What causes ALGAE problems?

Every pool owner has, at one time or another, done battle with the occasional algae bloom. Algae spores constantly enter the pool, brought in by wind, rain or even contaminated swimsuits or equipment. When conditions are right, an algae bloom can occur seemingly overnight. These conditions include out of balance water, warm temperatures, sunlight and presence of nitrates and/or carbon dioxide. Of course, a lack of proper circulation, filtration and sanitation may be the primary cause of the algae.

What problems can Algae cause?

The biggest problem algae causes is that no one wants to swim in it, making your pool useless. The second problem is that it requires work and effort and money to rid the water completely of algae. It is therefore best to use preventative chemicals and techniques. Algae can cloud and color the water, making rescue attempts difficult and reducing depth perception of a diver. Algae itself is not harmful to swimmers, but pools with algae may also harbor pathogens like E-coli bacteria.

In addition to clogging up sanitation pathways in the water, algae also clogs up the pores in a filter, decreasing filter effectiveness and requiring more backwashing or medium replacement. Algae creates a chlorine demand in the water for itself, actually consuming chlorine that should be working on other contaminants. Algae are kind of like weeds in your garden. Unsightly, unwanted space takers that create more work for the gardener, and sap up nutrients and resources from the flora we wish to grow.

What types of Algae are there?

There are over 21,000 known varieties of algae! In the pool business we avoid all of the complications by referring to algae by the color they exhibit.

1. Green Algae

An extremely common variety, green algae will usually rear its ugly head immediately following a hazy condition in the water from a lack of proper filtration and/or sanitation. It is frequently found free floating in the water, although it also will cling to the walls. It reduces water clarity and is thereby distinguished from severe copper precipitation, which will impart a clear, green color to the water. Varieties of green algae also appear as "spots" on surfaces, particularly rough areas, or places where circulation is low. They also show up as "sheets", where large wall sections, or even the entire pool, is coated in green slime.

2. Yellow Algae

A wall clinging variety, also called mustard algae, is usually found on the shady side of the pool. It is sheet forming, and can be difficult to eradicate completely. Once begun, a pool owner could spend the entire season fighting yellow algae; re-infection is common. This variety is resistant to normal chlorine levels and must be dealt with firmly by professionals who know what they’re doing.

3. Black Algae

The difficulty in black algae eradication is due to the strong roots and protective layers over top of the black algae plant. Black algae will appear as dark black or blue/green spots, usually the size of a pencil eraser tip. Their roots extend into the plaster or tile grout, and unless the roots are destroyed completely, a new head will grow back in the same place. The heads also contain protective layers to keep cell destroying chemicals from entering the organism. Like yellow algae, black strains can bloom even in the presence of normal sanitizing levels and proper filtration. This form of algae commonly enters a pool inside the swimsuit of a person who's recently been to the ocean.

4. Pink Algae

Not really an algae at all, but a form of bacteria. Appears as spots or streaks in corners and crevices. It is slow to spread and rare that it will bloom over an entire pool.

How is algae prevented?

Proper chemical balance and sanitizer residuals will prevent many opportunities for algae to bloom. high pH and low chlorine (or other sanitizer) can give algae a great start to genesis. General cleanliness of the pool is also important. Organic material and bacteria can contribute to algae growth. Regular brushing of seemingly clean pools is not only good exercise for you, but prevents dirt from harboring in the pores of the plaster, which is a good start for an algae colony.

The use of specialty chemicals or algaecides is recommended to provide a back up to normal sanitation and filtration processes and is completely necessary for many pools.

Potassium Tetraborate

This chemical, when added to the pool water in proper dosage, prevents algae from converting carbon dioxide into the fuel it needs for growth. Manufactured under the trade name Proteam Supreme. An extraordinary product.


Not an algaecide (meaning to kill algae) per se, but its properties might be called algaestatic (that is, to prevent algae growth). Chitin has the ability to coagulate and remove a wide variety of suspended materials and impurities from the water. This allows the sanitizer to more effectively kill contaminants unobstructed. It also improves the effectiveness of the filtration equipment. Sold under the trade name Sea Klear, chitin can be a valuable weapon in your algae arsenal.


Quaternary Ammonium Compounds

A low grade type of algaecide, Quats, as they are called, will usually have "10" somewhere on the bottle, representing 10% active ingredient. Although available at a lower cost, quats tend to produce a small amount of surface foaming. They are most effective as an algaestat, that is, as a prevention, not a cure.


Polymers are long, complicated chemical chains that behave in water both as an algaestat and an algaecide. They are available in percentage strength of 30 - 60%, are non foaming, and work well as general, all around algae treatments. Poly-Quats are a blended compound of polymer and quats.

Copper Based

Copper is a proven algaecide and algaestat. Available in varying non foaming strength of 3 - 10%. It works very well on all types of algae, but it has the drawback of staining white plaster surfaces a light blue/green color if it precipitates out of solution. Most copper based algaecides are chelated, which means that agents have been added to prevent this, such as Lo-Chlor Algaecide.

Silver Based

Silver has been shown to be an effective bacteriostat, which means that it works to prevent bacteria from reproducing. Non-foaming and effective with pink algae. In high doses, reactions with sunlight can cause colloidal silver to deposit as black stains on white plaster. When using copper or silver algaecides, the use of a sequestering agent is recommended.

Chlorine Enhancers:

These are not algaecides, but work to provide a synergistic boost to hypochlorites when added separately, but at the same time. Sold under trade names like Mustard Buster, Yellow-Out or Yellow Treat, it is most effective on, you guessed it, yellow algae. Since it is not an algaecide, the makers are not required to tell what it is made of, but we do know that it works quite well, in conjunction with a little brushing and vacuuming on your part.

How do I kill Algae?

Balance your water, paying particular attention to the pH. Keep it as neutral as possible, from a 7.0 to 7.4.Check your filtration system and clean it if necessary. Adjust the valving for optimal circulation and allow it to run 24 hours a day until the pool clears.Shock the pool for suspended green algae. Put in as much hypochlorite as it takes to turn the pool into a cloudy, bluish/gray color.If you cannot see the bottom of the pool, drain the pool, acid wash, and refill it.For algae clinging to the walls, brushing thoroughly is the most important thing you can do. For plaster pools, use a steel bristle brush. For vinyl, use a nylon brush.After brushing, use an algaecide, brush again, vacuum to waste, and then backwash the filter.

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