The most common causes of black algae growth in pools are insufficient chlorine levels, spores transferred by rain or wind and an improperly functioning pool filter. Immediate remedial steps help get rid of the algae before it spreads.
Chlorine helps keep the pool free of bacterial and black algae growth by maintaining the water's toxicity level above the tolerance of unwanted organisms. Exposure to sunlight accelerates the rate at which chlorine dissipates. When the level drops, black algae and other organisms have a chance to survive in pool water.
Dirt and leaves carry algae spores. The longer they clutter the pool’s bottom, the dirtier the pool gets, giving black algae a chance to thrive on pool surfaces. In particularly dirty pools, black algae continues to bloom despite boosting the chlorine concentration well beyond the recommended treatment level.
Pools with malfunctioning or clogged filtration systems quickly develop black algae problems. A sign of a possible pool filtration problem is the presence of milky or cloudy water. Lack of management of the problem quickly leads to an outbreak of black algae.
Manually spot cleaning black algae with a stiff brush and an algaecide or chlorine tablets helps curb its growth. Monitoring chlorine levels through water testing, vacuuming the pool regularly, ensuring filters are working and regular chlorine shock treatments help prevent algae growth.