How to Fix a Green Pool—in Six Simple Steps

Well, this isn’t fun. You might not typically associate swimming pools with the color green—unless you’ve personally experienced what high chlorine can do to blond hair and switched to a saltwater generator instead. And to be perfectly honest, it’s never good when your pool turns that green color. In fact, it signifies one thing and one thing only: green algae, which is the most common type and grows ridiculously quickly. Thankfully, it’s also the easiest of all algae to eradicate, but as with algae of any type, you’ll need to act now. I’ll explain how to get algae of out your pool with a combination of cleaning, chemicals, and circulation—and make sure it stays gone.

Okay, My Pool Is Green. So What?

Alright, stand next to your pool and look down. Are you sure you want to swim in that? And if you don’t feel like dealing with it right this moment, consider this: although the algae that occurs in pools won’t hurt you directly, it’s a killer for your chemical balance. Your sanitizer and chemicals will exhaust themselves working against it and have no strength left over for the other microscopic bad guys of your pool. And when that happens, the potentially harmful bacteria that your sanitizer is supposed to neutralize is surrounding you and yours on every swim. Not only does it look gross—and by the way, is gross—but it can also make you sick. On the same page now? Let’s get it out of there.

how to fix a green pool

Is It Really Algae Though?

Though a lot of maintenance issues might lead to a green pool, it’s green because it’s been infested with algae. It’s both maintenance mishaps and bad luck that allows algae to thrive. It can enter your pool if your chemical balance is off or your filter isn’t quite right, but it can also be introduced to your pool thanks to microscopic pieces on swimsuits and water toys.

To get a better sense of the amount of algae in your pool, first take a quick look at your pool’s surface. If your water is cloudy and has taken on a green hue, you’ve gotten a serious infestation of slimy algae floating in your water and attaching to your pool walls, steps, and floor. Next, check the corners of your pool—and this includes the hidden parts of your stairs. You might also see green spots around those covert areas. You’ll want to spend extra time on these trouble areas to make sure the algae is gone. 

How to Get Back to Blue Water—In Six Steps 

When it comes to sending algae packing, thoroughness is key. Take this as slow as you need, but you’re better off not skipping a step. Don’t forget: you’re up against a tiny, intrusive organism that grows fast and would rather stick around.

1. A Good Clean Runs Deep

Like an uncomfortable date, algae loves to cling. You’ll need to uproot it first before getting it out of the pool. Give your pool floors, walls, and steps a good, hard scrub using the patented BLACK + DECKER 360-Degree Bristles Pool Brush, which was developed by pool maintenance experts to help get tight corners without any of the aches or pains associated with a good clean. 

Once you’ve scrubbed your pool—especially those blooming corners, if you have them—remove large debris like leaves and twigs with a skimmer net on a telescopic pole, and then vacuum out all the algae to waste—or, if you’ve invested for the long haul, turn on your powerful robotic pool cleaner. Just be sure that you clean out any pool cleaner you use automatically. You don’t want any algae to circulate back out—or you’ll be here again in no time.

Seriously, the patented 3-Pack 360 Pool Brush Bundle is worth a try. It comes in 3 sizes for all parts of your pool and deck. Its design is the only one of its kind and was developed by long-term pool professionals. As customer Chastity notes, “I love these brushes, a size for every area, the cut out easily goes over jets, ensuring every surface in the pool gets clean.

2. Back to Balance—For Now

A green pool means algae has sucked up your sanitizer and other chemicals. Now’s the time to get your levels right, so that the pool shock you’re about to use has the space to really do its job. Pay special attention to are pH and alkalinity—if you have a high pH or a low alkalinity, it’ll prevent this next step from working. And don’t worry: we’ll test the water again when we’re through.

how to fix a green pool

3. Algae, Meet Pool Shock

Other sources might tell you that if you have algae, you need to use pool shock. And they’re right: it’s pool shock that’ll do most of the work to do the actual killing. But without these other steps, your shock won’t work as well, and it certainly won’t be enough to take care of your algae problem in any permanent way. 

Since you’ve scrubbed and vacuumed your pool and tested your water balance, your pool shock is ready to do what it was made for. For this green algae, you’ll need to shock at least twice as much as the average dose. Make sure you use conveniently-packaged one pound bags to know you’re using the right amount for your pool.

Just remember, as always, to shock your pool at dusk or night, so the sun doesn’t burn down your pool shock’s ability to work when you need it the most. And don’t swim for at least eight hours afterward—certainly not while your pool is still cloudy with shock. But you’ll be busy with this next step at first, anyway. 

Want to know how to clean the bottom of your pool? Read more here.

4. Filter Out the Green 

Immediately after pouring in your pool shock, you’ll need to run your pool filter and pump to make sure the killing chemicals are circulating. But first, check your water level. Since you just ran your manual vacuum or robotic cleaner, your water level could have dropped below halfway up the skimmer—and the last thing you want is for your circulation system to run dry in your moment of need. If your levels are in fact below where they need to be, fill up your pool with a garden hose.

Not sure how long your filter should be roaring? If you have the right pool pump and the right pool filter for you, an eight-hour run time should be perfect.

Poor circulation is one of the main factors that leads to algae infestations. If your pool pump isn’t cutting it, try the 1.5 HP Variable Speed BLACK + DECKER Pump. It’s robust, thorough, and the most reasonable decision any pool owner can make: it comes with a 5-year warranty, is eligible for rebates, and pays itself off in under one year.  

5. Test Your Chemicals, Part Two 

Whether you needed to top off your pool with a garden hose or not, you should take this moment to rebalance your chemicals again, and especially keep an eye on your pH and alkalinity. If there’s one thing that a green pool makes glaringly evident, it’s that algae can mess up your chemicals. Seriously. 

6. Clean or Replace Your Filter Media 

If your filter has unchecked microscopic deposits of algae, it’s going to circulate all those spores back into your pool. No, thank you. This is one of the common errors of pool owners, and one reason why some wonder why the pool shock they used didn’t work at all. 

To keep that algae gone, it’s a good idea to clean your filter, meaning a chemical rinse if you have a cartridge filter and a backwash if you have a sand or D.E. filter. But an even better idea? Just replace the filter media entirely.

Bonus Step: Algaecide is Your New Friend

Though you don’t have to, this is a great idea if your pool has gotten algae more than just this once. You might be wondering why I haven’t mentioned it before: that’s because pool shock is actually much more effective at killing algae. But algaecide is a great preventative measure. After you’ve cleaned and shocked and your chlorine level has fallen below 5 ppm, add a dose of algaecide and give your pool an extra scrub to make sure any microscopic algae spores are detached.

Did you know rain can also introduce algae spores into your pool? Make sure your cover is light and secure—and the rain is kept out of your pool—with the Sunnora 800 Standard Cover Pump. It’s fully submersible, comes with a specialized pre-filter to prevent clogging, and comes with a one year warranty. 

how to fix a green pool

Three Steps to Keep Algae Away

Algae is notoriously tough to keep out of your pool, and your normal sanitizer levels are simply no match for it. But there are routine measures you can take to prevent a future infestation, such as: 

1.     Shock every single week. It’s easy for pool owners to shrug their shoulders and skip this step, but if you have an algae problem, it’s just inviting trouble.

2.     Clean and sanitize all pool equipment and toys—before you let them into your water. Oh, and wash your swimsuit. In this case, a rinse under the faucet won’t do.

3.     Check your pool for cracks, breaks, or any kind of fun algae hideouts. You might need to resurface your pool, or do a bit of spot maintenance. 

You’re a Green-Killing Machine.

Now that your pool is back to being blue—and you can actually see the floor now—you can congratulate yourself on a job well done. The fact of the matter is that pool algae presents a problem for swimmer safety, even if the plant itself isn’t toxic. So let’s make sure it stays gone. And if it does come back, you’ll know exactly what to do. Enjoy.


For additional information on how to get rid of mustard algae, check out this article. Having problems getting rid of white water mold in your pool? Read more here.

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