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How to Get Rid of Pool Algae

Is your pool water green? Do you always have green pool water no matter what you do? Does it seem like there’s no way to get rid of the algae in your pool?

Well, you’re in luck, because we have the best and proven ways to get rid of pool algae fast!

Pool Algae: 3 Proven Ways To Get Rid Of It Fast!

First, let’s learn a little bit about algae and how it’s formed. According to the Merriam-Webster dictionary, pool algae is:

…a plant or plantlike organism of any of several phyla, divisions, or classes of chiefly aquatic usually chlorophyll-containing nonvascular organisms of polyphyletic origin that usually include the green, yellow-green, brown, and red algae in the eukaryotes and especially formerly the cyanobacteria in the prokaryote.

In other words, algae is a small plant-like organism which grows in pool water. And there are three common forms:

  • Green or blue algae
  • Yellow or mustard algae
  • Black algae

1. Green Pool Algae: Easy to Get Rid Of

Green algae is the most common form of swimming pool algae because it grows from lack of proper sanitation and filtration. Sometimes you’ll see green or blue algae free-floating in your pool water which causes your entire pool to look green.

You may also see this algae clinging to the walls or the bottom of the pool. It’s easy to brush off and mix into the water. The good thing about this green algae is that it’s easy to get rid of it. And it may only show up in little spots in your pool that have poor circulation, in which case a little sanitizer or algaecide will do the trick.

2. Yellow Pool Algae or Mustard Algae: Difficult to Kill

Yellow algae (or mustard algae) is stingy and grows on the pool walls that don’t get a lot of sun. It’s the second most common algae you’ll find, and it can often be mistaken for sand or pollen.

You cannot kill yellow algae with an average dose of sanitizer (i.e. chlorine) or an algaecide. You need to SUPER shock your swimming pool with a high dosage of chlorine, or else you’ll be battling it all season long.

How to Get Rid of Mustard Algae in a Pool

Got mustard algae? Here's a very simple tutorial that will walk you through how to remove stubborn mustard algae from your swimming pool.

3. Black Algae: Very Hard to Get Rid Of

Black algae is the incredibly stingy, but the good news is it’s not very common. What makes this algae so hard to get rid of is its defense mechanism and strong roots. Black algae looks like little dark black spots on your swimming pool wall.

The part that you can see has a protective layer to protect itself, and the roots are strong and grow deep into your pool walls. Just like yellow algae, this strain can appear even if you are taking care of your pool frequently and all your sanitation levels are correct. To kill it, you’ll need a heavy-duty pool brush and lots of chlorine shock.

How to Kill Black Algae in Your Swimming Pool

Black algae is perhaps the hardest algae to get rid of. Follow this step-by-step tutorial to help you get rid of black algae in your pool fast.

Why Do I Have Green Pool Water?

Where there’s water, there’s algae. Swimming pools need to be treated with chemicals to ensure nasty bacteria and other growths don’t get into our water.

The main reason why algae blooms grow in your pool is lack of sanitation. When your pool lacks proper sanitation, and the water isn’t circulating, algae will grow. That’s why it’s important to keep the pool water moving with your pump and filter – it’Iis difficult 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.

Method #1: Get Rid of Pool Algae by Superchlorination (Shock)

There’s three different stages of algae:

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

The more algae in your pool water, the darker the color will be. I’ve seen pools almost black with a green algae infestation!

Do You Have Light Green Pool Water?

If you have a light green pool, you need to double shock your pool. One 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 two 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’ll 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’ll 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)

Cal-Hypo Chlorine Shock (24-Pack)

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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 the most effective.

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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.

How To Shock Your Swimming Pool

Method #2: 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

Super Floc Out

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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.

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How to Floc 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.” Your 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).

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.

How To Vacuum Your Swimming Pool

Method #3: Use 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

In The Swim Pool Algaecide 60 Plus - 1 Quart

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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.

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Which Method Is The Best?

All of these 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 Method 1. It’s cheap, it’s easy, and it KILLS all the algae. I use Method 2 when I’m in a pinch like a family party is happening THIS WEEKEND, oh no!

How to Clear a Green Pool in 5 Days or Less

With a little work and these easy steps, you can easily clear a green pool in 5 days or less.

7 Tips To Keep Pool Algae From Coming Back

Here are a few vital tips for pool algae control to keep it in check all season long.

1. Keep Your Filter Clean

Keeping your filter clean helps in the circulation and removal of fine particles from your pool water.  Think of your filter as your lungs and you are a runner, if your lungs are clogged up you can’t breathe easily and your running ability is cut way back.  The same goes for your pool filter, for if it is clogged up the water can’t get through easily and your recirculation is cut way back.  This gives algae the advantage because the spores are not being filter out fast enough.

The same goes for your pool pump, think of it as your heart.  Again if your heart isn’t pumping to its full capacity your body can’t function to its best.  If your pool pump strainer basket is clogged your circulation is reduced, your filter isn’t working to its capacity algae gets the upper hand.  Always clean your pump strainer basket after vacuuming through your pool skimmer.

2. Keep Your Water Balanced

Water balance is important and should be checked weekly.  Maintaining a 1.5 – 2.0 or higher ppm level of free chlorine is important to keep water clear and sparkling.  Ph is also very important as the higher the ph reading the less effective your chlorine is.  Remember as nitrogen enters your water through swimming and landscape debris you start to form chloramines, this is the strong chlorine order you smell from your pool water is useless in fighting algae blooms.  Super shocking once a month during summer is suggested to keep your combined chlorine level down and your free level up.

3. Keep Phosphates In Check

Phosphates are food for algae, phosphates are in the runoff water from landscaped areas, some are by-products from what you add to your pool.  This is food for algae and should be monitored quarterly and reduced or eliminated on a regular basis.  The laundry soap you use for washing clothes and bathing suits contains trace amounts of phosphates, it all adds up to promote algae blooms.  Test and eliminate on a regular basis.

4. Keep Shocking Your Pool

Sometimes pool algae gets the upper hand and when it does super shocking and or using algaecides is necessary.  Brush your walls and floor to put the algae in suspension and super shock and/or add algaecide to knock it back, be sure to clean your filter once your water has cleared.  When using any metal based algaecide such as silver or copper use a sequestering agent to keep the metal in suspension to reduce the risk of staining your interior surface.

5. Keep The (UltraViolet) Light On

The use of UltraViolet or Ozone will help prevent the growth of algae from the spores it produces.  UltraViolet destroys the DNA and RNA chains of the algae and it dies unable to reproduce, Ozone will oxidize the spores and kill them on contact.  I prefer UV over Ozone because it is much easier to maintain in the long run.  These two systems will also reduce the amount of chlorine you need to add to your pool giving you a much nicer body of water to swim in.

We addressed chloramines above, super shocking will oxidize them and rid your pool of these nasty things.  UV will help reduce monochloramines so the di and trichloramines can’t form to begin with.

6. Keep Your Pool Sanitized

Remember as the weather warms up so does the demand for sanitation.  The UV rays from the sun are always trying to remove the chlorine from you pool water, bather load takes its toll as well along with warmer water.  Sometimes it is necessary to increase your normal addition of chlorine on a weekly basis to twice the amount you used in the winter.  Remember to test your water weekly and add as necessary to keep your water crystal clear.

7. Keep Cleaning

Don’t forget to brush your walls down and vacuum your floor, this is where an automatic pool cleaner is handy as it is cleaning your floor on a regular basis, however you still need to brush your walls and steps, dirt and debris can build up on the surface too small to see with your eye, and is a source of food for algae.

Happy Swimming!

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Last Updated: Sunday, July 28th, 2013