Pools can turn green after rain due to an increase in the number of algae spores that are present in the water. Rain can wash algae spores into the pool from the surrounding area, where they can then grow and multiply. Additionally, heavy rain can also cause the pH level of the pool water to fluctuate, which can create an environment that is more conducive to the growth of algae.
The chlorines level can also decrease during heavy rain, which can contribute to the growth of algae. Finally, heavy rain can also cause a large amount of debris to enter the pool, which can provide a food source for algae. This is why it’s important to keep the pool cover on during heavy rain to reduce the amount of debris that enters the pool.