Does Pool Algae Die In The Winter?

You might be wondering if it’s okay to close your pool in the winter without cleaning it. After all, most plants can’t survive in the cold temperatures, and if algae is one of them, cleaning seems unnecessary. But before you make any big decisions about closing your pool for the winter, let’s consider whether algae can be left behind.

Although pool algae can’t grow when the temperature drops to below 40˚ Fahrenheit, it may become dormant and grow again the moment the temperature begins to rise. There’s also no guarantee it will die completely in the winter, which is why it’s important to get rid of it before closing your pool.

When spring finally comes around, you’ll be eager to get back into the pool — and the last thing you want is to remove the cover to find a mess inside. So let’s look at how to prepare your pool for winter, how to keep it clean during the winter, and how to keep algae at bay.

Should You Close Your Pool Without Cleaning It? 

Swimming pool with plastic cover against snowy building houses and mountain

There’s a general assumption that two things will kill algae (and therefore there’s no need to clean your pool before closing it): a lack of light due to the pool cover and low water temperatures.

It’s true that when the water temperature drops, the algae growth will be stunted. The lack of light due to the pool cover will definitely help this. However, leaving the pool ‘green’ can cause stains and damage to the pool walls and equipment, which is the last thing you want to find when you open up the pool again in the spring.

Furthermore, the chemicals in the water will have to work hard to eat up the algae and you may find there are none of those chemicals left by the time you reopen the pool. That means the algae will have had time to form in stagnant water that’s run out of chlorine.

Will Pool Algae Die in the Winter? 

Although there’s some truth to the idea that algae won’t thrive during the winter months, it’s important to note that there’s a difference between no growth and the algae dying completely. Pool algae is unlikely to die in the winter, contrary to popular belief.

Instead, what happens is that the growth stops, and there’s no new algae formation over the winter months — as long as you live in a place with consistently cold winters. What happens when the temperatures start to rise though?

At that point, the algae begins to grow again, which is why it’s best to get rid of it before you close the pool in the first place. 

Tips On Preventing Pool Algae in the Winter

There are a few ways you can prevent pool algae from forming in the winter. Here are few that we recommend:

Shock the Pool Before Closing It

“Shocking” is a process whereby you add chemicals (usually chlorine) to pool water to quickly raise the chlorine levels and kill off algae and bacteria. Shocking your pool is critical to prevent algae from forming.

You can buy chlorine (on Amazon) and use around 3-5x the normal amount you would put in your pool to kill off any bacteria in there and leave the pool water nice and clean.

Use an Algaecide

Algaecide (on Amazon) is specifically formulated to kill algae in the water, so using this before closing your pool may be one of the most effective methods to prevent growth.

Clean Your Pool Cover Before Use

Before you put a pool cover over the water, make sure the cover itself is clean. If it’s covered in leaves and debris and then you throw it over the water, there’s a high chance these things will fall into the water and create more bacteria.

Leaves and other substances may also disintegrate into the pool when it rains, going through the cover if it’s not secure enough.

Run the Filter

Even though your pool isn’t in use, running the filter every day can be a huge help in preventing algae. Algae likes stagnant water, so making sure you run the filter will keep it at bay.

How to Maintain a Clean Pool in the Winter 

Girl hand holding mini water testing test kit over blurred swimming pool background

Once you’ve taken preventative measures to ensure that algae doesn’t have an inviting environment to form in during the winter, it’s important to maintain the cleanliness of your pool as well. Here’s how to do that.

Keep an Eye On It

The simplest tip for maintaining a clean pool in the winter is to keep an eye on it. If you put a pool cover over the water and walk away for the entire season, you won’t notice if there are any problems developing.

Every few days, you should take the time to look into the pool and scoop away any debris or break up sheets of ice that may have formed on top of the water.

If you don’t clear away ice sheets in the pool, they can thicken and eventually cause damage to the pool.

Maintain the Water Level

Maintaining the water level is also important, as this will help prevent ice from forming and debris from getting into the pool as a result. 

Test the pH and Chemical Balance

Every now and again, it’s also a good idea to test the pH and chemical balance of the pool. The pH should be around 7.2-7.4 and you should try to balance this out if it’s off.

It can seem like a hassle, but if you keep checking, the pool will be spring-ready when you open it back up.

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