Why does pool water turn green? The short answer is that it‘s caused by algae. Algae are tiny plant–like organisms that live in water and can reproduce quickly. When there‘s enough sunlight and nutrients available, they can grow quickly and cause the water to turn green.
There are a few things that can contribute to algae growth in pools. One is the pH level of the water. If the pH is too high or too low, it can create conditions that are favorable for algae growth. Another is the presence of nutrients like phosphorus and nitrogen.