Did Your Pool Turn Green After It Rained? Here’s How to Fix It

Written by Michael Dean
November 16, 2023

steps to fix a green swimming pool after rain

Rain can cause many frustrating issues with a pool since it carries a lot of unwanted debris that can upset the delicate chemical balance of your swimming pool. A common occurrence after a bout of heavy rainfall is green water, which is a frustrating and undesirable sight for every pool owner. If you’re looking for solutions for handling a green pool or are just curious about how to fix it if it occurs, look no further.

In this article, I’ll be going over why a pool turns green after rainy weather, how you restore it to its crystal clear state, and how to prevent it from turning green again.

Main Takeaways

  • A pool is at risk of turning green after a rainstorm since rainwater might contain algae spores, bacteria, and other contaminants that can damage the chemical balance of your water.
  • Shocking your pool and adding a phosphate remover are surefire methods of restoring your pool to a crystal clear state.
  • Swimming in a green pool is unsafe because of the potentially serious health hazards algae poses to the human body.

Why Does My Pool Turn Green After Rain?

There are several causes for water turning green, but if it’s directly after a rainstorm, there are usually three major reasons:

Algae Spores and Contaminants 

Rainwater isn’t the cleanest source of water around, especially nowadays. By the time the water reaches your backyard, it will have passed through several layers of toxins, chemicals, dust, pollutants, pollen, and more. Rainwater can also contain algae spores and other bacteria that can contaminate your pool.

When the rain hits the surface of your water, hundreds of algae spores are deposited into the pool. Don’t underestimate algae. In the right conditions, where the water is warm or stagnant, algae can replicate as quickly as 3 to 6 hours. This can make turn pool water cloudy and green in a single day.

Chemical Dilution

As rain falls into the pool, it dilutes the water, lowering the chemical levels. Rainwater dilutes the levels of cyanuric acid, chlorine, calcium, alkalinity, and sanitizers used to treat pool water. The dilution makes it even easier for algae to gain a foothold in the water, with the conditions just right for it to thrive and flourish rapidly. A green pool becomes inevitable in such a scenario.

Poor Circulation

A third major cause of green pools is poorly circulated water. The stagnant pool becomes the perfect environment for algae growth if the water isn’t filtered and circulated well. Poor circulation can occur when the pool’s pump and filter are dysfunctional, your cartridge filters are dirty, or there’s a leaky valve or a clogged impeller. It’s crucial to maintain proper circulation in the pool – especially after a rainstorm. And during – you shouldn’t turn off your pump while it’s raining.

In summary, rainwater can turn a poorly circulated pool green by diluting good pool chemicals while adding algae spores and harmful bacteria in their place.

Step-By-Step Guide: How To Fix Green Pool Water After Rain

Here’s my handy step-by-step guide to fixing green pool water after a bout of rain.

Step One: Test the Water

As with any pool issue, the first step is diagnosis. When fixing a green pool after rain, you have to test the water to determine the levels of chlorine, pH, and total alkalinity (TA). Grab your pool test kit to determine if the chemicals are within the recommended levels.

Step Two: Shock the Water

If chlorine levels are low, shock the water and kill off any algae that may be present. Shocking involves adding a hefty dose of chlorine to the water, killing off foreign bacteria and other debris, which helps restore your pool. Pour the recommended shock dosage into your pool at a steady pace while walking around the edge of the water.

Step Three: Run the Filter

Make sure your filter is in tip-top shape. If it’s not working, you’ll need to fix the filter before shocking the pool. If your filter is running correctly, run it for at least 8 hours after shocking the water. If your filter is struggling to remove finer particle matter, you could add a flocculant to clump up the debris and remove it manually using a pool vacuum.

Step Four: Balance the Chemicals

After shocking the pool and running the filter, balance the chemicals in the pool to ensure they are within the recommended range. Adjust the chlorine, pH, TA, calcium hardness, and other chemicals as necessary. Ideally, your chlorine levels need to be between 1 to 3 ppm (parts per million), and your pH needs to be between 7.2 to 7.6 for your pool to be a safe swimming environment.

Step Five: Use a Phosphate Remover

If your pool does not become clear after following these first few steps, you may have a pretty serious algae infestation. At this point, test your pool’s phosphate levels. Phosphates are a natural food source for algae, and high enough levels can overpower even highly chlorinated conditions, allowing algae to flourish even after a pool has been shocked. Although ideally, you’ll have no phosphate in the water, anything below 500 is acceptable.

If your phosphate levels are high, use a phosphate remover to combat the problem before attempting another pool shock. After adding the required amount, don’t forget to run your filter for another few hours to help circulate and filter.

Step Six: Use an Algaecide

And finally, I’d suggest adding an algaecide to your water to fully eradicate any lingering traces of algae, especially if the spores are particularly persistent.

How To Prevent Green Pool Water After Rain

It’s better to prevent your water from turning green after rainwater in the first place than to deal with the hassle of fixing a green pool. Here are a few points you can follow to prevent it from occurring again:

Get a Good Pool Cover

This is a relatively simple yet highly effective solution. Using a good quality pool cover goes a long way when preventing rainwater (and the contaminants it carries) from entering the pool. A pool cover also reduces the amount of sunlight reaching the water, allowing chlorine to work more effectively and making it less likely for algae to grow.

Circulate the Water

Proper circulation is key to preventing a green pool after rain. Keep an eye on your filter in case it needs DIY maintenance, such as dirty pool filter cartridges requiring a soak or replacement. In addition, ensuring the pool’s pump and filter system are in good shape is vital to a healthy and clear pool.

Regularly Clean the Pool

Regular cleaning of the pool will help to remove sneaky algae spores that the filter hasn’t caught. Develop a habit of brushing the walls and floor of the pool now and then, vacuuming, and skimming the water’s surface with a net to help your filter run more effectively. If you’ve got no time for that, you could also consider purchasing an automatic pool cleaner.

How To Fix Cloudy And Green Pool Water After Rain 

Your pool may look cloudy after rain since rain is acidic, which can wreak havoc on your pool chemistry. The easiest and quickest way to sort out cloudy and green pool water after rain involves balancing the water and clearing it of debris by using a skimmer net and flocculant. Shocking the pool may be necessary if your pool is particularly cloudy and green.

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Can You Swim in a Green Pool?

Swimming in a green pool is not at all safe. Ingesting water infested with algae or having it come into contact with the skin or eyes can result in eye or skin irritation, itchy rashes, and respiratory problems, among other issues.

More serious side effects of swimming in a green pool could involve severe allergic reactions that could be fatal. Other risks are possibly severe eye infections. For example, corneal ulcer, an infection that causes long-term, partial loss of vision or even complete blindness, is often caused by bacteria or algae and is a very real possibility for swimmers if they swim in an unsanitary green pool.

In short, I strongly don’t recommend swimming in a green pool due to the potential health risks associated with the presence of algae and other contaminants in the water.

Questions? Let me know.

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