How to Troubleshoot a Swimming Pool That Is Green After a Rainstorm

Test the pool water for pH and levels of either chlorine or bromine. When heavy rains and storms come, the rainwater that is dumped into the pool can unbalance even pools that are regularly tested. If the levels are off, this can allow microorganisms to multiply in the water and can account for the sudden green color. Chlorine readings should be between 1 and 3 parts per million while bromine should be between 2 and 5 parts per million. An appropriate pH level is between 7.2 and 7.8.

Scrub the sides of the pool. Often, the green color that develops after a rainfall is from algae; and if this is the case, any of the green stuff that is clinging to the sides should be slippery and will scrub off easily.

Add an algaecide. Blue-green algae dumped into the pool by the rain is one of the most common causes of a pool turning green after a storm, so adding an algaecide will most likely solve the problem. Use a type of algaecide specifically designed for blue-green algae; at the same time add whatever other chemicals are needed to return the proper balance and levels to the pool, such as chlorine or bromine for sanitation.

Wait for a few days after following the above steps. The algae should clear up by then if that was the only problem.

Test for nitrogen if the green color is still present after adding algaecide to the pool water. The rain may have also brought a nutrient with it that is impacting the balance of the pool. Nitrogen can also be carried into a pool by the rain and will encourage the growth of algae. Testing for the presence of nitrogen is something that can be done by a commercial pool store or sometimes a college extension office by taking in a water sample. For continued, post-rainstorm problems, it is worth taking this extra step to determine if nitrogen from nearby agricultural areas or fertilizers are continuously getting into the pool.