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Algae and Algaecides


Algae are microscopic single celled forms of plant life that are introduced into the water by wind and rain from the atmosphere. There are 30,000 different varieties of algae all containing chlorophyll. They are one of the hardiest and most widespread living organisms on this planet.

There are three main categories.

Green Algae: -usually floating algae though they sometimes cling to walls This is also the fastest growing algae and accounts for most 24 hr algae blooms Pool water becomes turbid with a green growth that renders the pool uninviting and dangerous to use as it is difficult to see the bottom of the pool. Prior to the green coloration appearing, the sides of the pool have a slippery feel and the water becomes hazy and exhibits a high chlorine demand..

Mustard (Yellow) Algae: -appears as a yellow powdery deposit on the pool, usually on the shady side. Once established, it is chlorine resistant and can exist in the presence of 3-5 ppm free chlorine. This is also a common algae which grows in aquariums in areas that get little light.

Black (Blue-Green) Algae: -evident by the formation of dime to quarter sized black (or dark blue green) spots, tenaciously adhering to the pools surfaces. Black algae forms a layered structure where the first layer (which chlorine may kill) protects under layers from further destruction. Black algae is similar to the black algae that is found on bathroom shower tiles and in silicone seams near the bath. It is also found in aquariums as dark blotching on the glass sides This form of algae is very slow growing but very hardy. It is extremely chlorine resistant,.

An algae bloom can turn clear clean water into a green swamp overnight. The pH can climb (as algae consumes carbon dioxide which helps keep pH down), and the pool walls become slippery and hazardous underfoot. Once algae is visible a substantial problem exists. Algae takes in carbon dioxide and gives off oxygen like most other plants. Most bacteria found in swimming pools take in oxygen and give off carbon dioxide. Each consumes the by-products of the other for growth. It is desirable to use a chemical program that assures both bacterial and algae control.

Prevention of algae

A proper chemical program of regular pool maintenance prevents algae from growing This means keeping the proper pH and recommended free chlorine residual for your pool. The best algaecide (algae killer) and algaestat (algae inhibitor) is a properly maintained sanitizer level of 1-3 ppm chlorine or 2-5 ppm bromine for a pool and 3-5 ppm chlorine or 3-6 ppm bromine in a spa. Algae is very rare in most spas and hot tubs as the "insulating hard cover" does not allow enough light for the algae to get a foot hold. Algaecides are chemicals added to the pool water to control algae. While algaecides can kill algae at high dosages, most are utilized as algaestats, which prevent algae formation when chlorine is allowed to become depleted.

There are three main groups of algaecides:

Quats:- the largest selling, lowest priced algaecides. These are most often found in active concentrations of 5-10%. Such "quaternary ammonium salts" are surfactants and if added in excess, will cause foaming on the pool surface. Surfactants lower the surface tension of the water and "wet" algae cell walls. This "wetting" splits open the cell wall and kills the algae. Quats require lower concentrations and amounts than polyquats to achieve the same level of prevention. Quats are most often used as the preventative while polyquats are most often used to get rid of existing algae.

Polyquats:-are non foaming algaecides sold in concentrations of 30 to 60%. While more costly than quats, polyquat algaecides are very effective not only on green algae but also with the chlorine resistant mustard and black algae and work well at destroying visible algae.

Copper Salts:-Copper ion (Cu+2) is a very effective algaecide used in ponds, lagoons and pools to kill and prevent algae formation. Copper usage can cause stain formation. Over time, soluble copper salts can precipitate from pool water and deposit on pool walls, creating a "blueing" effect. In the presence of chlorine, these salts will turn to cupric oxide and cause grey to black staining of the pool walls.

Colloidal Silver:- Silver is similar to copper in may ways, colloidal silver attaches itself to the pool walls and floor, giving these surfaces a residual and continuing algaecidal action. Silver can also cause a black staining to occur on pool walls if not carefully administered. Silver is also a very good bacteriostat that may reduce the need for chlorine. Some ionizers use copper and silver plates to produce both silver and copper ions in the water.

To Treat Algae.

Step 1
To treat algae once they taken control of a pool check pH and adjust if necessary. Check filtration, filter pressure and backwash if necessary.

Step 2
For green algae you can use one of two methods or implement both. Superchlorinate the water with up to 30 ppm chlorine. If necessary, 24-48 hours later when the chlorine drops to normal levels, add a good all purpose algaecide according to package direction. The next day, vacuum the dead algae and backwash the filter if necessary. Use of a good "Floc" can help speed up the settling of dead algae. In the case of heavy algae growth it may be necessary to repeat the treatment. After algae have been vacuumed, check pH, adjust if necessary, and institute a program of superchlorination and use of a good all purpose algaecide. Make sure the chlorine level is maintained at proper level to help prevent reoccurrence.

For Black or mustard algae. Brush the algae spots vigorously with a stiff brush. Shut off the pump, and use chlorine tablets to spot treat the algae spots carefully (not recommended for vinyl lined pools). Then pour a good concentrated all purpose algaecide on the algae spots. Leave dissolved algaecide in contact with the algae overnight. Restore water circulation, then brush dead algae and vacuum to waste. In case of heavy algae growth it may be necessary to repeat treatment. After algae have been vacuumed, check pH, adjust if necessary, and institute a program of superchlorination and then use a good all purpose algaecide. Make sure chlorine level is maintained at proper level to help prevent reoccurrence.

Prepared by Trevor Croll,

42 Pearse Street, Keperra, Queensland Australia, 4054.
Phone 61 7 3855 1115