Commercial Clearwater Company, Inc.

Algae is a living aquatic organism that multiplies rapidly in warm temperatures. Algae contains chlorophyll and grows through the process of photosynthesis. Algae spores are constantly entering pools, brought in by wind, rain or even contaminated swimsuits or equipment. When conditions such as unbalanced water, warm temperatures, sunlight, or the presence of nitrates exists, an algae bloom can occur seemingly overnight. Algae growth is facilitated by poor circulation, filtration and sanitation.

The first noticeable problem is the dirty appearance of pool water. The second problem is that it requires a great deal of effort to completely rid the water of algae. Algae itself is not harmful to swimmers, but pools with algae may also harbor pathogens like E-coli bacteria. Algae also clogs the filter, decreasing its effectiveness and ability to remove contaminants. Algae also creates an increased chlorine demand, so more chlorine needs to be fed into the pool.
There are over 21,000 known varieties of algae! The most common found on pools include:

An extremely common variety, green algae will usually appear immediately following a hazy water condition caused by poor 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, appears as "spots" on pool surfaces, or as "sheets" where large wall sections, or even the entire pool, is coated in a green slime.
YELLOW ALGAE: A wall clinging variety, also called mustard algae, is usually found on the shady side of the pool. It forms sheets on surfaces and can be extremely difficult to eradicate completely. This variety is resistant to normal chlorine levels and must be dealt with agressively. Yellow algae can bloom in the presense of normal sanitizing levels and proper filtration.
BLACK ALGAE: Perhaps the most aggravating strain of algae, Black Algae is extremely difficulty to eradicate due to its strong roots and protective layers over the 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.
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 rarely blooms over the entire pool.
Proper water balance and sanitizer levels will prevent the opportunity for algae to bloom. General cleanliness of the pool is also important, since organic material and bacteria can contribute to algae growth. High pH and low chlorine (or other sanitizer) can give algae a opportunity to bloom. Regular brushing of seemingly clean pools prevents dirt from building up in the pores and crevases of the plaster, where Algae colonies can get a start.
The use of algaecides (Algae killers) and algaestats (Algae preventers) provides a back up to normal sanitation and filtration, and for many pools in some locations is a necessary routine . Such chemicals include:
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.
CHITIN: Chitin acts as an algaestatic due to its ability to coagulate and remove a wide variety of suspended materials and impurities from pool water. This allows the sanitizer to more effectively kill contaminants. It also improves the effectiveness of the filtration equipment.
1. QUATERNARY AMMONIUM COMPOUNDS: Also called Quats, this is a low grade algaecide.
2. POLYMERS: 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 polymers and quats.
3. COPPER BASED: Copper is a proven algaecide and algaestat. Available in varying non foaming strength of 3-10% copper works well on all types of algae. Copper 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.
4. SILVER BASED: Silver has been shown to be an effective bacteriostat, which means that it works to prevent bacteria from reproducing. It is 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.
These are not algaecides, but provide a synergistic boost to hypochlorites. Sold under trade names like Mustard Buster, Yellow-Out or Yellow Treat, they are most effective on yellow algae.
First of all, balance the pool water, paying particular attention to pH. Secondly, check the filter system and backwash and clean if necessary. Ensure optimum circulation and run continually until the pool clears. Backwash as necessary.

For suspended green algae, shock/superchlorinate the pool. Brush the walls and floors, vacuum, and filter continuously. Backwash the filter as necessary.

Following superchlorination, allow the chlorine level to fall 5 ppm and add an algaecide. Brush the pool again. When it all settles, vacuum the pool to waste. Check the water chemistry and rebalance if necessary.

For algae which is not suspended, but only clinging to the walls, follow the same advice above, first shock, brush, then add an algaecide, brush again, vacuum to waste and backwash the filter. Use of a steel bristled brush is recommended for algae on plaster pools. Use nylon brushes on vinyl.

For black algae, the brushing part is very important. The plant's protective layers must be destroyed so the chemicals can destroy the plant from the inside out. Pumice stones work well to knock off the heads of black algae. Also try sprinkling granular trichlor over the spots (of course if they're on the wall this is next to impossible). Rubbing the spots on the walls with a trichlor tablet or stick may be effective in knocking off the heads and getting trichlor directly to the roots. Follow up with a dose of copper algaecide or high strength polymers.

If the algae is resistant to all of these measures, or has been a persistent ongoing problem, the pool may have to be drained. Acid wash and/or pressure wash plaster and marble dust surfaces to remove the algae roots imbedded in the plaster. Then change the sand in a sand filter, or the cartridge if the filter is a cartridge type. For a DE filter, remove the elements, spray clean, soak in a 10:1 water/bleach solution, rinse and replace the D.E. powder.