How to Clear a Green Pool

Maybe it’s been a while since you took a dip in the pool, but as soon as you decide to go swimming, you notice that the water in your pool is looking greener than your lawn. It’s not healthy or safe to swim around in green water, but clearing the water might also seem too overwhelming. The longer you wait, the problem will only get worse.

Cleaning up debris and keeping the water clear is an essential part of being a pool owner, but tackling a pool full of green water might seem like a task that’s out of your expertise. If your water has turned an ugly shade of green, don’t worry, it can happen to everyone. The best way to prevent green pool water is to know how and why it happens.

Why Did My Swimming Pool Turn Green?

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The color green in your pool means you have one enemy: Algae.

Algae is a simple plant, one that thrives in water that offers them food, and a hospitable (welcoming) environment. It doesn’t take much for algae to enter your pool. Algae can become airborne, or ride into your pool on debris, a swimsuit, or pool toy. When it finds water with nitrogen and phosphorus, that isn’t protected, algae start eating, and the bloom can seemingly appear overnight.

Interestingly, how deep the color is, ranging from “light green sheen” to “swamp murk greeny-brown,” gives you some of the information you need to fight it. We’ll get to that in just a minute, but more importantly, how did it happen?

A Few Reasons Why Algae Invades Pools

The simple, but annoying, reason for a green pool is usually due to the lack of sufficient water testing and sanitizer. When your pool’s sanitizer and chlorine levels fall below optimal levels, or the chlorine becomes entangled with other chemicals in your pool, you open the door to your tiny green nemesis.

The sanitizer makes your pool inhospitable to algae and kills it.

If you’re not testing often enough and not adding enough bromine or chlorine (or whatever type of sanitizer you use), you’re at a high risk of getting algae in your pool.

But you test regularly, all the time, you say? Well, that’s not always enough.

Mother Nature rarely keeps to our schedules, and your testing regimen is another one she’ll ignore. Many things make your pool more likely to need extra testing, as they make algae blooms more likely.

  • Extreme Heat/Weather Changes
  • High Winds
  • A Dirty Pool (debris makes for algae food!)
  • Incorrect pH Levels
  • Clogged Pool Filter

If any of these things are occurring in your area or your pool, you are more likely to face an algae bloom, and you want to test more often. Daily or every other day isn’t going to be too much.

Step-by-Step Guide: How to Clear Green Pool Water

Here are some essential steps to clearing your pool water.

1. Assess the Situation: Do You Need to Drain It?

Nobody wants to drain their pool if they can help it. To know whether or not you have to drain, start with this question:

On a scale from “a greenish haze” to “I think a swamp thing lives here?”: How green is green?

I’ve found, if you can see more than about the depth of a grown man’s spread hand (about 8 inches) into the water, chances are it’s not a lost cause. That means that you probably won’t have to drain your pool. If, however, you can’t see that far into the water, you may need to drain, and acid wash it.

You can, however, try to clear the green pool water first, before choosing the nuclear option. You can check your filters here too, and clean them up for the next step if you wish.

2. Test the Ph Levels

You can test the sanitizer level, too, but facing facts we already know that’s too low, which is why you have green water in the first place. You need to test your pH levels, and they make kits that make this as simple as possible and then get them on track.

If you don’t balance the pH levels, shocking your pool will leave you with very cloudy water. While cloudy water is expected in the short-term, as the shock does its job, balanced water won’t stay cloudy after the filtering process.

You can get pH adjustment chemicals to handle this task, up or down, but you’re going to want it at or below 7.2.

3. Time for Shock ‘n Awe

It’s time to shock your pool, and by shock we mean super chlorinate. You’re going to be adding a lot of chlorine. Even if you normally use a different sanitizer to wipe out algae, you need to fight dirty.

How dirty? We’re talking 30 ppm (parts per million) of liquid chlorine. Even though it might seem like a lot, it’s just enough to break through and disrupt the algae’s nucleus, preventing it from reproducing as you’ve killed it.

Use your test kit, and get it to that number. This can take 5 pounds of granular shock or 10 gallons of liquid. (If you have a diatomaceous earth filter, use granular shock.)

4. Let the Filter Do the Work

Shocking your pool removes exactly zero algae. What it does is kill it, so you can then let the filter clean it out. No matter what type of filter you use, be it a cartridge, sand, or diatomaceous earth (DE) you’ll need to clean it out several times while it clears the water.

If you have a DE filter, you need to backwash it before you start the process, and add fresh DE.

Allow the filter to run for at least 24 hours, after the treatment. Then, you can scrub the pool when you clean the filter, and then let it run again. You are going to repeat that process until the pool is clear.

5. Proactive Final Step: Kill and Flocc

You may also want to consider adding a few things here to help the process. An algaecide, which also kills algae, and a flocculant (causes the dead algae to bunch up for easier filtering) added after a couple of hours of the chlorine circulating. You can also wait until you are pretty sure you got all of them, to be sure.

At this point, the extra steps may not seem worth it. However, if you still have any algae that you missed, it could bloom again fairly quickly. You don’t want that.

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Final Tips: Keeping Your Pool Water Clear of Algae for Good

If you want to keep the green murk held at bay for good, your best bet is testing. Test a lot, test every day, or every other day, when the weather is changing or you have a lot of people using your pool. Testing once a week may be enough, but the more you test, the more you know.

Finally, testing is not beneficial if you don’t also fix what needs fixing; keep your water balanced, your sanitizer optimized, and your filter clean and fit to control algae for good.

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