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

Having trouble with pool algae? If so, know that you're not alone. Green pool algae is the most common issue that most pool owners face, along with stubborn black algae (black spot) and mustard algae, following close behind.

In this article, we'll touch on all three, diving into (no pun intended) what causes them, how to prevent them and what you can do to stop the issue from coming back.

If videos are more your thing, below is one of our head technicians providing his point of view on the best way to rid your pool of algae. 3, 2, 1... Action!

Okay, back to the blog...

What is pool algae?

Simply put, algae is a small plant-like organism that grows in pool water. There are three common forms:

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

1. Green Pool Algae

Green algae is the most common form of swimming pool algae as it grows due to a lack of proper sanitisation and filtration alongside a high pH. Usually, you’ll see this algae floating in your swimming pool or on the pool walls, potentially causing your entire pool to turn green. 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 sanitiser (chlorine), hydrochloric acid or algaecide will do the trick!

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2. Yellow Pool Algae or Mustard Algae

Yellow algae is a type of algae that grows on the walls of your swimming pool in areas that don't receive a lot of sun. It’s the second most common algae you’ll find in swimming pools and can sometimes be mistaken for sand or pollen that may collect in your pool. This algae is difficult to get rid of and won’t be killed by any normal dose of a sanitiser such as chlorine or an algaecide. You need to kill it by super shocking your swimming pool (a high dose of chlorine and acid) or else you’ll be battling with it all season long! More on shocking your pool down below, or check out this in-depth guide on how to shock a swimming pool.

3. Black Algae

This algae looks like little dark black spots on your swimming pool wall. If you've ever had yellow algae in your swimming pool and thought that it was tough, think again. What makes black algae so hard to get rid of is its strong defence mechanisms and strong roots. The part that you can see has a protective layer and the roots are strong, growing deep into the plaster of your pool walls. To kill it, you will need a strong pool brush and lots of shock (chlorine and acid). Specific chemicals, such as Black Spot Remover, are extremely concentrated and handy for removing black algae.

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Why Do I Have Green Pool Water?

The main reason why algae grows in your pool is because it hasn’t been treated with a sanitising chemical, such as chlorine, or hasn’t been treated enough, and your pH is probably a little high. Algae eats high pH water for breakfast, lunch and dinner. Also, when your pool is lacking sanitisation and the water is stagnant, you’re likely to see algae form. That’s why it’s important to keep the pool water moving using 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 pool ladder
  • On your pool steps
  • In all corners, creases and crevices

 

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

How Do I Get Rid Of Pool Algae?

Method #1: Get Rid of Pool Algae by Shocking Your Pool Water

There are usually 4 basic steps involved in shocking a swimming pool:

  1. Sanitise your pool with a heavy treatment of chlorine, either granular or liquid. Ensure that non-stabilised chlorine is used.
  2. Lower your pH with hydrochloric acid or pH Down Tablets. By doing this, the chlorine will be more effective.
  3. Ensure the system is on and running for a 24 hour period to disperse the shock treatment around the pool. Clean the pool filter of any debris captured.
  4. Test and re-balance the water two to three days later and make any additional adjustments required. Switch the filtration system back to its normal operating procedure.

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Different Colors mean different stages of algae growth

There are three different stages of algae growth in which different amounts of pool shocking are required, which are:

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

 

So, let's expand on them all below.

Light Green Pool Water

If you have a light green pool, you need to shock your pool in order to kill algae. Algae feeds off high pH levels and chlorine isn't as effective when your pH is high. You will need to lower your pH using hydrochloric acid. Start off with 1 to 2 litres. Be careful when adding it to the pool, ensuing it doesn't splash on you as it is highly toxic and dangerous. Only add 1 litre 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. Use 2 cups (400 grams) of granulated chlorine (not stabilised) or 3 tubs of 15L chlorine (it's only 20% chlorine and the rest is water). If your pool is salt water chlorinated, you'll want to add 2 to 4 bags of salt and turn your chlorinator to 100% for a couple of days to really boost the chlorine levels and get the water sanitised.

If you've added your salt and turned your chlorinator up to 100% but, after a few days, there's still no, or next to no, chlorine being produced or your ‘low salt’ light, your electrode may need replacing. An average lifespan for an electrode is three to five years. You also will need to clean your cartridge filter or backwash your sand filter, ensuring all your skimmer baskets and pump baskets are empty.

Once your pool is sparkling, don't forget to add 500g to 1kg of Stabiliser/Cyanuric Acid/UV Blockout to prevent evaporation, keeping the chlorine in the pool.

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Dark Green Pool Water

If you have dark green pool water, you should follow the above steps, but with a slightly higher dose of acid and chlorine. Adding, for example, 2 to 3 litres of acid over a space of 48 hours and 2 to 3 cups (600g) of granulated chlorine.

Also, darker green water may also be a cause of stagnant debris at the bottom of the pool which needs to be cleaned out before you dose it. Be sure that this has all been scooped up using a leaf shovel before manually vacuuming out of the pool using a vacuum head, the appropriate length hose for your pool (9m, 11m or 15m) and a telepole.

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Black Green Pool Water

If you have a Creature from the Black Lagoon green pool, you’ll be looking at doing the ‘Light Green Pool Water’ dosage, as outlined above, x3. This may take some filtering and cleaning or backwashing of the filter, followed by more filtering to complete the clean up process over a period of 2 to 3 weeks. Black green pool water will almost certainly have stagnant debris sitting on the bottom of the pool, whether it be leaves or a creature that got stuck and never made it out, and this needs to be cleaned out before you dose it. Be sure that this is all scooped up using a leaf shovel, before being manually vacuumed out of the pool using a vacuum head, the appropriate length hose for your pool (9m, 11m or 15m) and a telepole.

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Note: If you have a vinyl lined 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.

Need more details on how to manually vacuum your pool? Check out this guide on how to vacuum your pool manually here.

Method #2: Floc Your Swimming Pool

Floc (or flocculant) is a chemical which takes all the small particles in your pool (such as 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 involves more work and can be time consuming, but gets rid of algae fast if done correctly.

Note: We do NOT recommend this method if you are using a cartridge filter as it will clog your filter cartridge element. If you do, be prepared to buy a new filter cartridge element.

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Step-by-step guide on floccing your swimming pool:

1. Set your filter to "Recirculate' or 'Recycle'.

If you have a multi-port alve on your filter, shut off your pump and turn the valve to ‘Recirculate’ or ‘Recycle’. This will stop the water from flowing through the filter. All this does is to spin the water around, helping to 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. Let the water circulate for at least two hours.

Circulate the water for about 2 hours to ensure the flocculant is 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. Set your vacuum multiport to 'Waste'.

Hook up your manual vacuum cleaner. Before you turn your filter on, make sure you have your multiport 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.

If you have a cartridge filter, unfortunately you do not have this waste option and all waste will go through your cartridge, more than likely clogging that cartridge filter element and leaving it needing to be replaced. We do not recommend floccing your pool if you have a cartridge filter unless you plan on replacing the cartridge filter element when you're done. This can be quite pricey, at anywhere between $60 and $150.

5. Add your garden hose to the pool and turn it on while you vacuum.

Since you are vacuuming using the 'waste' setting, you’ll lose a lot of water from 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 a thick, dirty sludge out of your pool, and, as you move the vacuum across the pool floor, it’s going to start to kick up debris. When it becomes too 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 do this several times, depending on how much debris you need to vacuum.

When you are done vacuuming the pool and everything looks good, we would suggest double shocking (2 to 3 litres of acid over a space of 48 hours and adding 2 to 3 cups (600g) of granulated chlorine) your pool to make sure ALL the algae has either been removed or destroyed.

Need more details on how to manually vacuum your pool? Check out this guide on how to vacuum your pool manually here.

Method #3: Use A Pool Algaecide

There are some good algaecides which directly kill algae, though they are almost all a glorified combination of chlorine and acid. These algaecides may have to be added in large doses, and depending on the brand, 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 levels should also do the trick.

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You can add 200mL every week to prevent algae from growing in your swimming pool. 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 can cause staining.

How Do I Stop Algae From Coming Back?

Remember the old saying "An ounce of prevention is better than a pound of cure?" This is so applicable to your pool. Keep your pool from getting sick (algae!) and you'll never have to worry about the extra expenses trying to revive it.

Keep your pool in top shape and algae-less by doing some periodic maintenance, it may be a bit time-consuming, but it is worth it in the long run.

Don't have much time? Don't worry, it doesn't take too long if you follow our tips and tricks on how to test and fix your pool water.

Which Method Is Best?

We would choose Method #1: Getting Rid Of Pool Algae By Shocking every day of the week. By using this method, you're keeping it simple by focusing on chlorine and acid, while using your filtration system to bring it back to life. It tends to be a bit of a work-in-progress and can take 1, 2 or even 3 weeks, depending on the state of your pool, but it's definitely the easiest.

We also personally like to recommend keeping an algaecide on-hand year round for monthly dosage. If your pool is clear and balanced, an algaecide will do its part in keeping any green, black or mustard algae bay during a chlorine or pH fluctuation.

Do you have any questions about this topic or the featured products? No worries, we're here to help! Head over to our Contact Us page and drop our friendly team of pool pro's a line. 

Happy swimming :)

Featured Products throughout this blog

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Please 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 or harm caused by adding chemicals. Please practice common sense to add chemicals safely to your pool.

Do you have any questions about this topic or the featured products? No worries, we're here to help! Drop us a question down below and we'll get back to you ASAP.

Happy swimming :)

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Post author:

Natalie Hintze

Head of eCommerce & Marketing at Mr Pool Man,
Co-Founder at Water TechniX

2 comments

  • good advice thanks

    Walter R RHODES on

  • Hi my name is Deidre and our pool is green. I have had a sample down to our local pool shop and they gave me some chemicals and what was needed but it is still green. Can you please give me some advice on what else we can do to fix the pool. Thankyou
    Regards
    Deidre Farrow

    Deidre Farrow on

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