What Makes the Water in a Pool Turn Green when It Rains?

Insufficient chlorine is one of the most common reasons pool water may turn green after it rains. However, there are some other things that could happen to contribute to discolored or green-hued pool water following a rainstorm. Below, we get into this topic in a more detailed way and offer tips on how to deal with and prevent this problem.

Lowering Free Chlorine Levels

“Free chlorine” is the amount of chlorine in your pool’s water that hasn’t yet combined with chlorinated water. In other words, it’s how much chlorine is left to get rid of the microorganisms rainwater can add to your pool water. Because rain is nonchlorinated, it dilutes the water in your pool, which reduces the amount of free chlorine available. Under these conditions, algae growth is more likely to occur even in a salt water pool, which can leave you with green water after it rains.

Throwing Off Your Pool’s Chemical Balance

Rain does more than just lower free chlorine levels. If we’re talking about a particularly heavy downpour or even a few days of intermittent rain, the chemical balance in your pool could be thrown out of whack. For example, if a heavy rainstorm kicks phosphate levels up too high, you could end up with cloudy or green pool water.

Bringing Environmental Contaminants into Your Pool

It’s not unusual for in-ground pools to be near landscaped areas or spots where there’s soil that can be easily washed away when it rains. These materials can also get into your pool and create the perfect environment for algae growth. Pollution, phosphates, and various organic elements in rainwater can further contribute to pool water contamination. Once your pool’s pH levels are altered by these various contaminants, algae spores can quickly multiply. This can happen quickly, so you might end up with green pool water the day after a significant or steady rainfall.

Preventing Water Discoloration after It Rains

The most effective way to deal with pool water turning green after it rains is to prevent it from happening in the first place. Luckily, there are some steps you can take to boost your odds of achieving this goal. The ones we recommend include:

• Using a durable, solid, and secure pool cover
• Regularly cleaning your pool and removing any debris
• Checking the chemical levels after it rains if your pool is uncovered
• Draining some water from your pool if a heavy rain increases water levels too much
• Running the pump after it rains

Dealing with Green Pool Water

If your pool’s water has already turned green after a rainfall, check the chemical levels. If chlorine levels have significantly dropped, add enough to restore balance. Do this with other chemicals you might need to adjust as well. You may also need to shock your pool to kill off the algae. In some instances, it may take a few days and more than one treatment to fully get rid of any remaining algae spores in your pool.

Whether they need expert advice on maintaining their pools or they’re looking for a premier pool contractor, San Diego ca residents should reach out to the team at San Diego Pools. We’ve been designing and building pools for almost half a century, and we pride ourselves on our innovation and outstanding craftsmanship. To get started on your new pool, give us a call today at 888-707-7786.