How To Get Rid Of Green Algae In Pool Water

Algaecide Dos and Don'ts for Saltwater Pools: Tips from Pool Maintenance Experts

Why Is My Salt Water Pool Turning Green?

When your pool turns green like pea soup, you already have an algae problem in all likelihood that needs quick fixing. Upping the chlorine won’t fix it and neither will shocking the pool.

Green algae in your pool requires algaecide to kill the algae but you also need to fix the water chemistry as you undoubtedly have a low (or no) chlorine problem.

Figuring out how to get rid of green algae in pool water is easier when you tackle it the moment you see if rather than waiting and hoping it’ll go away. I can speak from personal experience. But if you’re already past that stage, no worries. Let’s talk about how to get rid of it for good.

How To Get Rid Of Green Algae In Pool Water & What Causes Algae Anyways?

Algae spores can be blown into your pool, it can come from rain or other sources but will not survive when the chlorine level is high enough and you have good water chemistry overall. But if chlorine levels are low and algae is able to survive, it’ll start to multiply.

Algae tends to grow in pool water during two distinct times perhaps not surprisingly and for slightly different reasons:

  • When the pool is closed for the winter
  • During the summer when the pool is open and being used

When The Pool Is Closed

Closing your pool early can cause algae to grow over the winter.
Closing your pool too early can cause algae to grow over the winter.

Over the winter when a pool is closed for the season, the entire system is shut down so no chlorine is produced and the pool is not being sanitized. If you close your pool too early when the temperatures are still around 65°F or 18°C or warmer, you run the risk of having an algae-filled pool come spring. Let me tell you from experience.

Being a first time pool owner in 2006, my wife and I were completely new to the pool-owning experience and figured things out on our own along with a bit of help (but not as much as I’d have liked with hindsight) from our pool company. Their suggestions were good at time but I mostly ended up figuring stuff out myself.

Here’s what I learned on how to avoid green algae in the spring time when you rip the winter cover off your pool and get ready to open it for summer:

Get The Chemistry Right Before Closing

One week before closing, start getting the pool ready by ensuring your chemistry is correct. Get the right chlorine, pH levels, etc. Either test the water yourself or take a water sample into your pool company.

Super Chlorinate When Closing

When closing your pool, shock or super chlorinate it a day or two before closing. Our second pool company dumped chlorine in on the day of closing, right before they put the winter cover on. In our case, it means adding about 6 gallons (20L give or take) of liquid chlorine to get the chlorine level up high, right before closing. I learned from our second pool company the importance of adding chlorine at closing to keep the pool sanitized and prevent algae build up. Our first pool company never did this.

And we ended up with green pea pool water every single spring. And a week of me trying to get rid of it.

NOTE: If you’re adding chlorine on the day of closing, dump the chlorine in after you’ve drained the pool to flush out the lines if you live in a winter area where freezing occurs. No point in adding chlorine and then pumping water out!

Use An Algaecide

We add one bottle of algaecide into the pool shortly before closing too. Either the day before or day of. If there is algae starting to grow in the pool, the combination of high chlorine and algae killer should keep it at bay. Chlorine alone won’t kill algae, even high amounts of it. I found that out the hard way too. As with the chlorine, dump the algaecide in after pumping water out of the pool, if pumping is needed.

When The Pool Is Open

How to get rid of green algae in pool water during the summer: Pool use during the summer along with low chlorine levels can cause algae to grow.
Pool use during the summer along with low chlorine levels can cause algae to grow.

The second reason algae tends to appear is when the pool is open in the summer and being used. This is typically a case of there not being enough chlorine in the pool. The problem is that once significant algae has set in, super chlorinating or shocking the pool won’t help. You’d have to dump a crazy amount of chlorine in to kill the algae.

Not only would that be expensive and probably fruitless, it’s not great to use significantly high amounts of manufactured chlorine in a salt water pool as it can damage the chlorinator cell.

Use An Algaecide

Instead, when you already have algae growing, use an algaecide as per the instructions and required amount (depends on the volume of your pool) to kill the algae. You’ll start to see algae sitting on the bottom of the pool as it dies and then you’ll have to rinse or backwash your pool filter to get rid of it. It often looks cloudy and gray.

Rinse Or Backwash Filter

You might want to rinse the filter and then rinse again a few days later after the algaecide has done its thing. You may need to use algaecide again for bad cases.

While you’re doing this, ensure your chlorine level and other numbers are correct because it’s likely you have no chlorine or too little chlorine being produced.

Brush, Vacuum, Rinse/Backwash

Once the algae starts dying, brush the sides and bottom of the pool to loosen algae and let it go through the filter and out of the pool. Vacuum the pool to get rid of the dead algae as well. Like I said, keep an eye on the filter as vacuuming, rinsing and backwashing will help to get the dead algae out of the pool system completely but it can get stuck in the filter and clog it up. A dirty filter can also cause dead green algae to come back out the water return jets into the pool.


  • How to get rid of green algae in pool water is a matter of getting the water chemistry (chlorine especially) correct, adding an algaecide, brushing the pool to get rid of remaining algae, rinsing or backwashing the filter and repeating if necessary.
  • Algae growth can occur when you close a pool too early (in the winter/spring) and it can also occur in the summer (when the pool is being used). Lack of chlorine is the problem.
  • Chlorine alone will not kill algae and it’s not good to consistently dump large amounts of chemical chlorine in a salt water system as it damage the salt cell.
  • Check out my page on 10 Tips To Winterize A Swimming Pool to learn more about pool closings and how to avoid algae in the process.

Carl Mueller

I bought a home with a salt water pool in 2006 and soon realized the benefits over traditional chlorinated pools. On this website I'll discuss all the tips and tricks I've learned over the years. I'll also help you troubleshoot various problems with pools in general and ones specific to salt water pools that I've experienced personally!

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