How to Get Rid of Algae in Swimming Pools

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Why Do I Have Green Pool Water?

Where there’s water, there’s algae. Which is why swimming pools need to be treated with chemicals to ensure nasty bacteria and other growths don’t get into our water.  Learn how to get rid of Algae in Swimming Pools.

The main reason why algae grows in your pool is because it hasn’t be treated with a sanitizing chemical, like chlorine, or hasn’t been treated enough. Also, when your pool is lacking sanitation, and the water is stagnate, you’re gonna get algae. That’s why it’s important to keep the pool water moving with your filter and pump. It’s hard for algae to grow when the water is moving.

Algae also loves dark places that don’t get much water circulation including:

  • under your ladder
  • on your pool steps
  • all corners, creases and crevices

These are all great spots for algae to feed and multiply.

So now that we have a general understanding of what pool algae is and why it forms, we must destroy it!

Method 1 How to Get Rid of Algae in Swimming Pools: Superchlorination (Shock)

There are 3 different stages of algae in which different amounts of shock are needed, there is:

  • Light green algae
  • Dark green algae
  • Black green algae

These are not different types of algae, it’s just different amounts. The more algae in your pool water, the darker the green color will be. I’ve seen pools almost black with an algae infestation. Gross!

Light Green Pool Water

If you have a light green pool you need to double shock your pool in order to kill algae. 1 pound of shock treats up to 10,000 gallons of water. So, if you have a 10,000 gallon pool or less you will need to double shock it by adding 2 pounds of shock.

If you have a 20,000 gallon pool or less, you need to add 4 pound bags of shock. And if you have 30,000 gallons or less you need to add 6 pound bags, and so on.

Dark Green Pool Water

If you have a dark green pool you will need to triple shock it. So, if you have a 10,000 gallon pool or less you will need to add 3 pound bags of shock.

If you have a 20,000 gallon pool or less you need to add 6 pound bags of shock and if you have 30,000 gallons or less you need to add 9 pound bags, and so on.

Black Green Pool Water (Creature From The Black Lagoon)

If you have a, “Creature from the Black Lagoon” green pool you will need to quadruple shock it. So, if you have a 10,000 gallon pool or less you will need to add 4 pound bags of shock.

If you have a 20,000 gallon pool or less you need to add 8 pound bags of shock and if you have 30,000 gallons or less you need to add 12 pound bags, and so on.

Cal-Hypo Chlorine Shock (24-Pack)

List Price: $52.99

It’s a good idea to buy your shock in bulk to save money and so it’s always on hand. This shock has a very high amount of active chlorine which is perfect for killing algae. Remember always shock your pool at night when the sun is gone for it to be its most effective.


Note: If you have a vinyl liner pool, you should dissolve each 1 lb. bag in its own bucket of water before putting it in the pool. This will prevent your liner from being bleached out by the shock. Also NEVER POUR SHOCK THROUGH THE SKIMMER IF YOU HAVE AN AUTOMATIC CHLORINATOR. We cannot stress this enough.Calcium Hypochlorite which is found in shock, mixed with trichlor, which is found in most chlorine tablets creates a deadly explosive green gas. And remember, always shock at night. Chlorine burns off 1 PPM (Part Per Million) every hour in direct sunlight causing the chlorine to drop below break-point oxidation required to kill algae.

Method 2 How to Get Rid of Algae in Swimming Pools:  Floc Your Swimming Pool

Floc (or Flocculant) is a chemical which takes all small particles in your pool (like algae) and settles them to the bottom. After all the particles have settled to the bottom, it’s your job to vacuum them OUT of your swimming pool.

This method is more work and can be time consuming, but gets rid of algae fast, if done correctly.

Super Floc Out

List Price: $18.99

Add this chemical to your pool, let it circulate for a few hours and watch as all the debris in your pool falls to the floor.


Here is a step by step guide on floccing your swimming pool:

  1. If you have a multi-port valve on your filter, shut off your pump and turn the valve to “Recirculate” or “Recycle.” This will stop the water from flowing through your filter. All this does is spin the water around to help mix the chemical in.
  2. Add the recommended dosage of Flocculant to your pool. Floc comes in liquid and powder form. Make sure you check the directions for the right dosage for your size swimming pool.
  3. Circulate the water for about 2 hours to get the chemical fully mixed in, then shut off your pump and let it sit overnight. During this time, the chemical will start to bind the particles together and settle them to the bottom of the pool. In the morning you should wake up to a nice healthy particle cloud at the bottom of your pool.
  4. Hook up your manual vacuum cleaner. Before you turn your filter on, make sure you have your multi-port valve set to “Waste.” When you vacuum this thick cloud OUT of your pool, you don’t want that thick water going through your filter. You filter will not be powerful enough to clear the water that fast, so cloudy (or green) water will just shoot back into your pool through the return lines. You don’t want this. Also, make sure you hook up your backwash hose to the backwash/waste port and direct the hose where you want your dirty water to go.
  5. Add your garden hose to the pool and turn it on while you vacuum. Since you are vacuuming to “waste” which will dump a lot of water out of your pool, it’s best to have your garden hose replacing the water with clean water as you vacuum out the dirty stuff.
  6. SLOWLY vacuum the bottom of the pool. You’ll be sucking out this thick, dirty water from your pool, and as you move the vacuum across the pool floor, it’s gonna start to kick up debris. When it becomes to cloudy to see what you’re doing, shut off your pump and let it sit for a couple of hours to resettle. Then you can go back and continue vacuuming. You may have to to do this several times depending on how much debris you need to vacuum (I told you it would be hard work).

With just little bit of elbow grease, and this cheap chemical, you can have your pool cleared in one day, if you’re willing to do the work.

When you are done vacuuming the pool and everything looks good, I would suggest double shocking your pool to make sure ALL the algae has either been removed or destroyed.

Method 3 How to Get Rid of Algae in Swimming Pools: Using Swimming Pool Algaecide

Normally algaecide, like pesticide, is only a preventive and should be used throughout the pool season. But there are some algaecides that contain b14 or metals, such as copper or silver, which can kill algae. These algaecides may have to be added in large doses depending on the brand, but mixed with shock, can do the trick just as effectively as just plain shock.

To be honest, I only recommend algaecide as a preventive. You can add a few ounces every week to prevent algae from growing in your swimming pool. The reason is, once you start talking about algaecides that can kill algae, the price starts going up. Also, you don’t want to add too many metals to your swimming pool. Metals in your water cause staining.

There are algaecides that are known as “poly quats.” These are great preventive algaecides that I recommend, but I would not use them in large doses to kill algae. They can cause excess foaming in your water.

To sum it up, some algaecides DO kill algae, but not all. Make sure you ask your local pool store which algaecides are the killing kind. Or make sure you read the specs carefully if you are buying an algaecide online.

In The Swim Pool Algaecide 60 Plus - 1 Quart

List Price: $23.99
I always recommend a high-concentrate algaecide like an Algaecide 60 Polyquat. It’s non-foaming and very effective for keeping algae from growing in your water.


Which Method Is The Best?

All of these how to get rid of algae in swimming pools methods work. In fact, you might visit three different pool stores or three different websites and they will usually just promote one way of doing it. This is why getting your pool care information from different places can cause confusion.

My recommendation is using how to get rid of algae in swimming pools Method 1. It’s cheap, it’s easy, and it KILLS all the algae. I use how to get rid of algae in swimming pools Method 2 when I’m in a pinch, like a family party is happening THIS WEEKEND, oh no!


How to Get Rid of Algae in Swimming Poolshow to get rid of algae in swimming pools


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