By far the most regular complaint of swimming pool owners is algae. This is because the algae is visible and unsightly. There are over 21,000 species of algae known to man but only a fraction of these are encountered in swimming pools.
Algae does not cause disease. It is a plant that turns sunlight and carbon dioxide into food and provides nutrients for bacteria which can then multiply rapidly (and may cause illness). When there is algae present in the pool water, the chlorine is used up rapidly trying to combat its growth. This process has a tendency to raise the pH, thus decreasing the efficiency of the remaining free chlorine. Algae is a living aquatic creature that multiplies rapidly on warm, sunny days.
Of course, a lack of proper circulation, filtration and sanitation may be the primary cause of the algae. The best process is one of elimination.
Unchecked algae growth can turn the swimming pool cloudy or makes the pool water green and results in foul odors and tastes. Black algae, which is more difficult to control than green or blue-green algae, can also stain the swimming pool's walls and floor.