How To Get Rid Of Pool Algae (Green Pool Water)

Having trouble with pool algae? If so, it's very easy to get rid of. Just follow these steps to kill pool algae and stop it from coming back!

Are you having a huge party and now your pool water is green? Or are you the kind of person who constantly has green pool water no matter what you do? Does it seem like there is no way to get rid of the algae in your pool?

Well you are in luck, cause we are about to explain…


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

"...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.


To simplify that, algae is small plant-like organism which grows in pool water. There are three common forms:

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


This is the most common of all the swimming pool algae because it grows due to lack of proper sanitation, filtration and high pH. Sometimes you’ll see this algae free floating in your swimming pool which can cause your entire pool to turn green. You may also see this algae cling to the wall of your pool, on the steps or at the bottom. It’s really easy to brush off and become free floating. The good thing about this type of algae is that it’s easy to get rid of. It may only show up in little spots in your pool that have poor circulation in which case a little sanitizer (chlorine), Hydrochloric Acid or algaecide will do the trick.



A stingy type of algae that grows on the walls of your swimming pool in spots that don’t get a lot of sun. It’s the second most common algae you’ll find in swimming pools and sometimes can be mistaken for sand or pollen that can collect in your pool. This algae is difficult to get rid off and won’t be killed off by any normal dose of sanitizer (such as chlorine) or an algaecide. You need to kill it by super shocking your swimming pool (high dose of chlorine and acid) or else you’ll be battling with it all season long.



If you ever had yellow algae and thought that was tough, think again. Black algae are the stinginess of all the algae, although the good thing is it’s not very common. What makes this algae so hard to get rid of is the defence mechanism it processes and it’s strong roots. This algae looks like little dark black spots on your swimming pool wall. The part that you can see has a protective layer on it to protect itself and the roots are strong and grow deep into the plaster of your pool walls. Just like yellow algae this strain can appear even if you are taking care of your pool normally and all your sanitation levels are correct. To kill it you will need a strong pool brush and lots of shock (chlorine and acid).

Also, specific chemicals like Black Spot Remover is extremely concentrated and handy for directly removing black algae.

Click here for our easy guide on How To Get Rid of Blackspot Algae.



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.

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, and your pH is probably a little high. Algae eats high pH for breakfast, lunch and dinner. 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!



There are 3 different stages of algae in which different amounts of pool shocking 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 colour 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 shock your pool in order to kill algae (add more Acid and Chlorine than usual). 
A lot of things can come into your pool being green therefore resulting in Algae growing. We would recommend getting your water tested at a local pool shop to know exactly what your pool is requiring as each and every pool is a different size, has different equipment set up to it and is made differently. But to keep it simple:

Algae feeds off high pH and your chlorine isn't as effective when your pH is high, you need to lower your pH using hydrochloric acid. 1-2L of it to start with. Be careful when adding it to make sure it doesn't splash up on you as it is highly toxic and dangerous, and only add 1L every 24 hours if your pool is Vinyl lined as it's more sensitive to harsh chemicals.

You also need to shock your pool with chlorine, 2 cups/400 grams of granulated chlorine (not stabilized) or 3 tubs of 15L chlorine (as it's actually only 20% chlorine and the rest is water), or if your pool is salt water chlorinated adding 2-4 bags of salt (once again you should get your salt tested at your local pool shop to see exactly where it's sitting) and turning your chlorinator to 100% for a couple of days to really boost that chlorine and get that water sanitized. Your salt should be sitting at around 5000ppm (parts per million) and each 20kg bag of salt equates to 500ppm.

If you've added your salt and turned your chlorinator up to 100% but after a few days theres still no or next to no chlorine being produced or your "low salt" light is still on even though you know there's plenty of salt in there, your electrode may need replacing. An average life span for an electrode is 3-5 years. You also will need to clean your cartridge filter or back wash your sand filter, and ensure all of your skimmer baskets and pump baskets are empty.

If the green in your water has set up home on your pool steps and doesn't want to move out (sounds like my mid-twenties children) adding hydrochloric acid should slowly start killing the algae on your steps as well, if your pool is concrete you can use a metal brush or if your pool is vinyl you can use a normal plastic bristle brush to help brush this algae off.

Mr Pool Man can't sell or ship Hydrochloric Acid, Liquid Chlorine, Granulated Chlorine or Salt online as it's either dangerous materials or too heavy, though you can grab them from your local pool shop.

We recommend testing your water a few days after this heavy dose to check your levels. You can do this yourself using a 7 in 1 Test Strip Kit.

Once your pool is sparkling, don't forget to add 500g-1Kg of Stabilizer/Cyanuric Acid/UV Blockout to keep that chlorine in the pool and not being sucked up by the sun. Adding 500g of Stabilizer once a month should keep this in check.

Dark Green Pool Water

You're looking at following the above steps but at a slightly higher dose of Acid and Chlorine. For example adding 2-3 Litres of acid over a space of 48 hours and adding 2-3 cups/600g of granulated chlorine. Also, darker green water may also be a cause of stagnent debris sitting on the bottom of the pool which needs to be cleaned out before you dose it. Be sure that this is all scooped up using a leaf shovel, followed by being manually vacuumed out of the pool using a vacuum head, appropriate length hose for your pool (9m11m or 15m) and a telepole.

Click here to read more about how to manually vacuum your pool.

Black Green Pool Water (Creature From The Black Lagoon)

If you have a, “Creature from the Black Lagoon” green pool, you will be looking at doing the "Light Green Pool Water" dosage as outlined above x3. This may take some filtering, cleaning or backwashing of the filter, and more filtering to completely clean up over a period of 2-3 weeks. Black green pool water will almost certainly have stagnent debris sitting on the bottom of the pool which needs to be cleaned out before you dose it. Whether it be leaves or a creature that got stuck and never made it out, be sure that this is all scooped up using a leaf shovel, followed by being manually vacuumed out of the pool using a vacuum head, appropriate length hose for your pool (9m11m or 15m) and a telepole.

Click here to read more about how to manually vacuum your pool.


Note: If you have a vinyl liner pool, diluting any chemicals that are being added to your pool in SEPARATE tubs of water (we don't want any chemical reactions here) is always a good idea to ensure no damage is done to your liner.



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.

We do NOT recommend this method if you are sporting a cartridge filter; it will clog your filter cartridge element to the point of no return. If you do, be prepared to buy a new filter cartridge element.


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.
If you have a cartridge filter, unfortunately you do not have this waste option and all this gunk will go through your cartridge, more than likely clogging that cartridge filter element up to the point of no return and needing to be replaced. We do not recommend floccing your pool if you are working with a cartridge filter, unless you plan on replacing that cartridge filter element when you're done, which can be quite pricey, anywhere between $60.00 - $150.00.


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).

Click here to read more about how to manually vacuum your pool.


With just little bit of elbow grease, and this cheap chemical and a bit of chlorine and acid, 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 (2-3 Litres of acid over a space of 48 hours and adding 2-3 cups/600g of granulated chlorine) your pool to make sure ALL the algae has either been removed or destroyed.



Normally algaecide, like pesticide, is only a preventive and should be used throughout the pool season. But there are some good algaecides which directly kill algae, though they are pretty much a glorified combination of Chlorine and Acid. These algaecides may have to be added in large doses depending on the brand and can get expensive. Unless you're using specific black spot algaecide for a specific black spot issue, Hydrochloric Acid dosing and bumping up your chlorine should do the trick.


To be honest, I only recommend algaecide as a preventive. You can add 200ml every week to prevent algae from growing in your swimming pool, but you shouldn't have this problem if your water levels are in check. The reason is, once you start talking about algaecides that can kill algae, the price starts going up. Also, algaecides tend to include metal bases, and you don’t want to add too many metals to your swimming pool. Metals in your water cause staining. 

To sum it up, some algaecides DO kill algae, but not all. If you're unsure you can drop us a line on 1300 511 901 or contact us.



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!

Happy Swimming!


Note: This blog is a rough indication of advice for an average sized pool and average dosing recommendations. Mr Pool Man always recommends getting your water tested by a pool professional before adding any type of chemicals for your own safety, or giving us a call on 1300 511 901 or contacting us if you are unsure. Mr Pool Man does not take any responsibility for incorrect dosages.


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