Algae comes in many species and subspecies, each with different causes. One common cause is improper chlorination. During summer, even one day without chlorine can lead to a significant algae bloom. Poor circulation and filtration also contribute. Without proper circulation, chlorine can’t do its job, and without effective filtration, algae spores remain in the water, ready to grow when exposed to the sunlight they need for photosynthesis.

    While chlorination is key, it's not just about adding chlorine. The pH level of your pool greatly affects chlorine’s effectiveness. The lower the pH, the stronger the chlorine. Another important factor is cyanuric acid, also known as conditioner or stabilizer. This is essential for your pool, acting like sunscreen for chlorine. Without it, chlorine will "gas off" within hours, leaving your pool vulnerable to algae growth due to lack of chlorination. However, too much cyanuric acid reduces chlorine efficiency, which can also result in algae growth ...read more here