How to Clear a Green Pool in 5 Days or Less

Have you ever thought it might be fun to dye your pool green for St. Patrick’s Day? Well, it would be fun until you had to clear the dye out of there, and restore the chemical balance likely disrupted by the foreign substance. So please don’t do that.

But sometimes, you might find you have a green pool without meaning to at all. That definitely won’t be any fun to swim in, or to look at. Don’t worry, though. All is not lost. You don’t have to drain your pool and start over. You can send that algae packing, and then take steps to keep it from coming back.

Why Do I Have a Green Pool?

When your pool water turns from a lovely shade of blue to a sickly green, there’s only one reason: pool algae. If it’s a light shade of green, the algae has probably just started to take hold. But a deeper green means a bigger problem.

Algae develops when the pool’s sanitizer levels are too low. If you haven’t been keeping up with pool water testing and water balancing, or you’re not adding enough chlorine, bromine, or whatever type of sanitizer you use, you’re practically laying out the welcome mat for algae to come in and make itself at home.

How to Clean the Green

Before you get started, gather a few supplies:

• pool vacuum head and vacuum hose
• algae pool brush
• test strips or a liquid test kit
• pool shock with at least 70% available chlorine

1. Vacuum to Waste

Once you start removing algae and debris from your pool, you obviously don’t want anything you take out to make its way back in. So your first step is to vacuum the pool to Waste.

Set the valve on your filter to Waste, then vacuum away, removing as much algae and sediment from the bottom of the pool as you can.

2. Brush the Pool

Rather than just your usual, regular pool brush, it’s best to use an algae brush for this task. Algae is tough, and will stubbornly cling to the pool’s surfaces, so a heavy-duty brush works better than soft nylon bristles to remove it.

Use the brush to scrub the pool walls, floor, steps, and any other surface the algae may be clinging to.

Note: You may be wondering, why don’t you brush the pool first, then vacuum it? Don’t you want to vacuum up the algae? No. No you don’t. You want to kill the algae, and it still has to be in the pool for you to do that. Trust us.

3. Test for pH and Alkalinity

Using test strips or a liquid test kit, test the pH and alkalinity levels. Note the levels as you’ll refer to them later.

If you want to, you can also note the chlorine (or other sanitizer) level. We’re willing to bet it’s going to be too low or even nonexistent. If the sanitizer level was where it should be, you wouldn’t be dealing with algae. It also won’t matter once you get to the next step.

Note: Testing the water could be the first step. If you’d rather test, then vacuum, then brush, go for it. It won’t affect the algae removal process.

4. Shock That Algae Right Outta the Pool!

This is the main event in clearing a green pool—killing the algae. Pool shock contains a high level of chlorine that will kill the algae and sanitize the pool.

For the best results, use a shock that contains at least 70% available chlorine, and shock the pool twice.

Important: Even if you normally use non-chlorine shock, you must use chlorine shock to kill algae.

If your pool is dark green, meaning you have a larger algae infestation, we recommend shocking the pool three times. And if the color of your green pool is reminiscent of a dark, spooky swamp, shock it four times.

Note: You may notice the pool water looks cloudy after shocking. Don’t panic. This is perfectly normal. But if you’re in a rush, you can add pool clarifier to speed up the process.

Zappit 73% Chlorine Pool Shock – 50 lbs.

$149.99

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5. Run, Filter, Run!

Once you’ve shocked the pool as many times as you’re going to shock it, turn the filter on, and don’t turn it off until the water is completely clear. Here’s where those five days or less come in. Be patient.

Again, you can use pool clarifier if you want to clear it more quickly, but even if you do, be sure to run the filter for at least 24 hours to get the dead algae out of the water, and ensure the shock has fully dissipated.

Clorox Super Pool Water Clarifier

$17.70

Your filter can clear a cloudy pool. But your filter needs help picking up particles that are too small. A clarifier binds these particles together, so your filter can remove them easier.

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6. Test, Balance, and Test Again

When your green pool isn’t green anymore, test the water, this time not just for pH and alkalinity, but also for sanitizer. Add chemicals as needed to balance things out. Test it again to make sure everything’s as it should be, and you’re ready to enjoy your pool again.

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How to Keep Algae From Returning

Now that your pool’s clear again, you want to keep it that way. The number one method to do that is to ensure you maintain proper sanitizer levels. This entails testing your water frequently, at least once a week, but we like to test about every other day.

If you notice levels are a bit on the low side, add sanitizer immediately. Don’t let algae get another toehold in your pool.

And if it will put your mind further at ease, you can add algaecide during regular water maintenance. But honestly, your best bet is just to stay on top of the sanitizer situation.

HTH Pool Algaecide Super Algae Guard 60 – Copper Free

$25.89

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But What About Phosphates?

You may have heard pool pros or other pool owners say that to control algae, you need to control pool phosphates, and use phosphate remover to do so.

We have one word for that: No.

No, you don’t need to worry about phosphates, and no, you don’t need to use phosphate remover.

Trying to remove phosphates from any environment is like trying to remove dust particles from the air. You will never, ever, ever be able to do it completely. Well, unless you build a clean room. The same is true for phosphates. They’re everywhere and in everything.

Yes, they’re a food source for algae. But to control pests in your vegetable garden, do you remove the vegetables? Of course not. You kill the pests. The same is true for algae.

Sanitize, sanitize, test, balance, and sanitize some more. And use the money you would’ve spent on phosphate remover on a nice pool float.

No Grinchy Green Here!

Opening your cover to a green pool may be disappointing. No, not “maybe.” It is. But never again will you feel defeated by algae now that you have the upper hand.

All it takes is a little hard work and the right chemicals, and you can kick that algae to the curb — er, the pool deck.

Happy Swimming!

Matt Giovanisci, the founder of Swim University®, started in the pool and spa industry at age 13 and moved to bigger companies along the way, helping thousands of pool and hot tub owners every year. He wanted to share his knowledge and unique teaching style on a larger scale, so he launched Swim University® in 2007. Since then, he's worked to make pool and hot tub care easy for over 10 million homeowners. And each year, he continues to help more people with water chemistry, cleaning, and troubleshooting.

Frustrated by adding chemicals and trying to keep your pool clear all the time?

We cut out all the confusion of pool maintenance in this easy-to-read illustrated ebook and video course. It'll help you save $100 right away on pool care!

Click here to learn more