Green Pool Algae: A Prevention and Cleanup Guide

Ryan Cuenca
April 29, 2019

If you take a DIY maintenance approach to your swimming pool, chances are you've arrived home from work or some time away and been greeted by the unsightly appearance of green pool algae.

You rush to your garage or shed to get some more chlorine, only to find you are fresh out, so you hop in the car down to the pool store, only to find they are closed! Meanwhile, the bacterial invaders occupying your pool water continue to spread and multiply.

Let's face it: As pool owners, we've all been here before. Green algae in your pool can be quite frustrating!

But the good news is that green pool algae (and all pool algae for that matter) is relatively easy to clean up, and even easier to prevent.

How to Prevent Green Pool Algae

While I will address how to clean up green pool algae below, I want to quickly spend a bit of time explaining how to avoid it in the first place.

After all, an ounce of prevention is worth a pound of cure, and I'm sure all of us would prefer a little preventative pool maintenance over the headache of a green pool. It can be time-consuming and expensive to clean up, especially if you are slow to address the problem. Furthermore, you can't (or shouldn't!) swim in it until it's gone!

By performing weekly pool service, you can stay on top of the conditions that allow green pool algae to flourish.

Green Pool Prevention Checklist

  1. Make sure your pool pump is operational. If your pump isn't working properly, you will get a green pool, guaranteed. Check out our blog article for a detailed description on the importance of pool water circulation.
  2. Run your pump for at least 8 - 12 hours a day. While this will vary based on a number of factors, if you are continually fighting a green pool, too short of a pump run time could be a factor.
  3. Clean or backwash your filters regularly. If you have cartridge filters, we recommend a cleaning every 6 months. Sand filters and diatomaceous earth (D.E.), every month.
  4. Make sure your pool has enough water. If you have an auto-fill, this shouldn't be an issue. But if you don't, check your water level regularly and make sure it is about halfway up a skimmer opening.
  5. Clean out all skimmer baskets, pump filter baskets, and automatic pool cleaner bags regularly.
  6. Remove all leaves and debris from the water surface and the bottom of your pool regularly.
  7. Brush the stairs, steps, and sides of your pool regularly.
  8. Test your pool water regularly, and ensure your water chemistry is properly balanced.

If you do these things consistently, chances are you will never have a green pool again!

How to Treat Green Pool Algae

For those past the point of prevention, fear not! Cleaning up green pool algae is a relatively straightforward task that requires a bit of elbow grease and patience.

Of course, green algae comes in many different shades. The deeper and darker your pool water is, the more effort it will take to clean up, but the basic procedure will remain the same.

Step 1 - Test Your pH Level

The very first step to getting rid of your pool algae is to test your water.

The reason is that a high pH level can make your pool shock less effective. If your pH reading comes in high, add pH reducer to your pool until your pH is at the right level. Once you've done this, continue reading!

Of course, if your pH is within the right range (7.2 - 7.8), no action is required. Continue reading!

Step 2 - Preparation

Make sure you have the following things on hand:

  • A properly functioning pump and filtration system that you know how to operate (if you don't know this, you may be better off contacting a local pool company for a green pool clean-up. We provide our customers with green pool cleanup assistance over the phone or via video chat.)
  • A pool brush suitable for your pool finish
  • Pool shock (continue reading for guidelines on how much you'll need)

Next, empty all your skimmer baskets, your pump filter basket, and your automatic pool cleaner bag (if you have one) and as much debris as you can from your pool. Leaving debris in your pool makes your system work harder and extends the amount of time it takes to get your water cleaned.

Now, ideally, wait until the sun is close to setting. If this isn't realistic for you, that's OK, just know that your pool shock won't be as effective in the sunlight. You can still get the same results, it just may take more time and pool shock.

Step 3 - Brush Your Pool

Brush every part of the pool that is underwater. Sides, stairs, steps...everything. Be as thorough as you can.

This will make your pool look like a cloudy mess. But don't worry: you've just put a whole bunch of algae in suspension where it will get zapped by the shock you are about to dump in.

Step 4 - Shock Your Pool

Before we get to the fun part, we must determine how much pool shock you should use. The amount of pool shock you use will be based on two factors: your pool size and how bad the green algae infestation is.

Determining Your Pool's Gallonage

Most pool owners (until a short time ago, the present author included!) have no clue how large their pool is. But it is a very helpful thing to know.

Why? Because most pool chemical manufacturers state dosage requirements in terms of gallons. If you don't know how many gallons your pool has, you can easily over or undersupply your pool.

We encourage you to find out your pool gallonage by a) contacting the original builder or b) using our online pool volume calculator.

Calculating Amount of Pool Shock to Use

Now that you know your pool size (or an approximation of it!), onto how much pool shock to use.

A maintenance (no algae) dose of shock is 1b and it treats 10,000 gallons. So, if you have a 20,000-gallon pool, you would use 2 lbs of shock for a maintenance dose.

But with green pool algae present, you need more than a maintenance dose. Here's how much more. If your pool water is:

  • Only slightly green and you can still see the bottom: x2 maintenance dose
  • Moderately green and you can't see the bottom: x3 maintenance dose
  • So green you can't see past the first few inches of the water: x4 maintenance dose

For example, if you have a 20,000-gallon pool and you can't see the bottom, you would use 6 lbs of shock. 2 lbs maintenance dose (20,000 gallons / 10,000 = 2) x 3 for algae strength = 6 lbs.

Now for the fun part. Following the manufacturer's directions for use, apply the recommended pool shock dosage to your pool. Close your eyes and listen carefully to hear the billions of algae colonies crying out in agony and despair.

Step 5 - Run Your Filter Pump

And keep it running non-stop until your green algae problem has vanished. This process will likely take a few days, depending on how severe your algae bloom was.

Make sure to brush your pool thoroughly every day to knock the algae back into suspension, where it can be destroyed and filtered out.

Step 6 - Clean Your Filter

Since you just put your filter through the ringer, it's time to clean it. Clean your filter thoroughly, either by rinsing it (cartridge) or backwashing it (sand, diatomaceous earth).

Step 7 - Test and Balance Your Water

Now that your water is algae-free, it's time to test and balance your pool water.

Step 8 - Enjoy Your Pool!

Now that your green pool is a memory, you can sit back, relax, and enjoy your pool.

Green Pool Algae Frequently Asked Questions

I followed Poolhop's green pool treatment plan, but my water is clear but cloudy. Is something wrong?

No. What are you seeing is dead algae that is still being filtered out. If you wish to speed up this process, you can buy a water clarifier (aka, flocculant). Otherwise, give it a few more days and it should clear up.

I was surprised that you didn't mention using algaecide in your article. Isn't it effective?

Algaecide is far more effective at preventing algae blooms than it is at treating them. Using an algaecide certainly won't hurt things, but pool shock should do the trick on its own.

When should I drain my green pool vs shocking it?

This is difficult to answer in general terms, but here are a few examples of when you might want to "drain the swamp".

  • The pool has been left unattended for a very long time and the water surface looks like a solid coat of green paint
  • Your pool filter is vastly undersized and won't be able to keep up with the filtration
  • If you are under the gun and don't have time to wait 3 - 5 days for your pool to clear up

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