Swimming Pool Algae
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.
Unchecked algae growth can turn the swimming pool cloudy or makes the pool water green and results in foul odours 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.
Prevention is better than cure. Adequate levels of free chlorine will prevent algae from growing out of control. When algae growth is noticed, it requires harsh treatment. Usually shock treatment with chlorine or an algaecide is recommended. If the pool has a mineral sanitiser such as the Pool Wizard installed, algae growth is a sign that you need a refill. Algae cannot grow in water sanitised with the Pool Wizard, provided the water is properly balanced.
More algae resources and discussions can be found at the Pool Algae Help Forum.