The growth of green algae in a swimming pool causes the water to appear green and is the result of improper pH balance of the water or accumulation of debris due to a clogged filter. Poor pool maintenance is a leading cause of green algae growth in swimming pool water, making it a breeding ground for fungi, mold and harmful bacteria.
Low total alkalinity in a pool, especially during humid or warm weather, causes bacteria and algae to thrive. Green algae growth gives the pool a cloudy green color and also causes green spots on the pool surface. A clogged filter system in the pool causes debris to accumulate, leading to thriving harvests of mold, fungus and algae. Green swimming pool water is an indicator that the pool is dirty and maintenance is overdue.
If chlorine levels in the pool water are optimal, check for high iron and copper levels in the water, which can also turn it green. If there is no chemical imbalance in the pool water, start by treating the water with low doses of algae remover, and increase it if needed. In cases of excessive green algae buildup, shock the pool with a large dose of algaecide and chlorine, and allow it to sit for 24 hours to kill the algae and bacteria. Clean the pool and filters thoroughly, and restore the pH levels of the water.