How to keep your pool algae free

October 26, 2023

Even the most spectacular of pools can look uninviting if not taken care of properly. Green, algae-filled water is the most obvious of these, but thankfully keeping your pool algae-free isn’t too complicated. Like most pool maintenance, it’s about performing small tasks regularly to avoid a larger problem.

Sometimes, life happens and we understand that too. In fact, with the right (or wrong) environmental conditions, pool water could even turn green overnight — it’s not necessarily the product of long-term neglect.

If you are dealing with a build-up of algae in your swimming pool, we’re also going to give you some helpful, actionable steps below. We’ll cover how to identify the type of algae and the steps you need to take for a pristine, swim-ready pool.

What is Algae?

The term algae is a catchall for aquatic organisms capable of producing oxygen through photosynthesis. Algae differentiate themselves from land plants with their lack of roots, stems, and leaves, and a vascular system and are commonly composed of just one cell!

They can exist on their own, bunch up to form multicellular clumps or take a leafy shape in the form of seaweeds like kelp. Algae can grow anywhere, saltwater, freshwater, or – you guessed it – the chlorinated water of pools.

Though algae does serve a key role in our ecosystem, we don’t want it in our pools! Not only does it ruin the aesthetic, but it can draw in potential bacteria and infections.

How to Prevent Algae from Growing in Your Pool

Prevention is always better than the cure. To help you avoid this build-up in the first place, it’s important to understand the basics, so let’s start there. If you stay on top of these each week, you’ll rarely have to do anything else to keep your pool water safe, healthy and looking great.

  • Algae can thrive in water that’s out of balance. If you can keep your pool’s pH level in check, you’re already halfway to keeping algae under control.
  • Stagnant water is also an ideal breeding ground for algae. Both actively using your pool and running your pool filter regularly keep the water circulating and avoid those stagnant conditions.
  • Keep your pool clear of debris. As leaves and other organic matter break down in pool water, it can upset the chemical balance and create an ideal environment for any algae that’s present. Vacuuming the floor and walls of your pool is all that’s needed when done regularly.
  • Make sure your pool filter is clean and running effectively. When it’s running regularly and well maintained, your pool filter can also help you remove smaller deposits and keep the overall health of your pool in check. Don’t forget, pool filters need maintenance too!

The different types of algae you might find in your pool

If your pool water or the hard surfaces are looking unhealthy, the first thing to do is determine what type of algae you’re dealing with. Three different types are most common in pools.

Green Algae

This is the most common type and the one most of us think of when we think about a dirty pool. You’ll find it both suspended in the water and on the surface and it’s what gives poorly maintained pools that green appearance.

While green algae itself isn’t harmful to humans in small quantities, other bacteria feed on and thrive in it. This means the potential for a wide range of potential health risks.

Yellow Algae (Mustard Algae)

To add more confusion, ‘yellow algae’ is a type of green algae. It gets its name from the yellow or brown (mustard) colour that can be seen on the hard surfaces of your pool. Like regular green algae, this variant isn’t directly harmful to humans but it must be taken seriously as it can help other, dangerous bacteria thrive.

You can typically find yellow algae on ladders or near pool lights. You can tell yellow or brown algae apart from dirt by its slimy texture. This type of algae grows in the shady areas of your pool that receive less sunlight. It is also highly resistant to chlorine which makes it difficult to get rid of.

Black Algae ( aka Blue Green Algae)

If you’re noticing dark spots forming on the hard surfaces of your pool, there’s a good chance it’s black algae. Since this can be a serious health hazard, it’s something that needs to be dealt with immediately.

According to SEQ Water, this algae can bring the following health hazards, depending on the exact species:

  • Swallowing water containing algae toxins may cause gastroenteritis symptoms such as vomiting, diarrhoea, fever and headache. The toxins produced by blue-green algae may also affect the liver, kidneys or brain.
  • Inhaling affected water may cause respiratory problems and flu-like symptoms.
  • Skin contact with water, including sensitive areas such as the eyes, ears, mouth and nose, may cause irritation, skin rash, flu-like symptoms, and fever.

Despite the name, black algae technically isn’t an algae at all, it’s cyanobacteria. In a swimming pool, it tends to form on porous surfaces where it can attach and form a root system. This makes it difficult to scrub off in the first place and, even when it’s no longer visible, it may be able to grow back.

How to Remove Algae from a Pool?

Now that we’ve covered the prevention and identification of pool algae, let’s look at what to do once it’s formed. The recommended steps vary depending on the type you’re dealing with.

Note: While you may be able to swim sooner, we recommend getting your pool both looking and testing safe and healthy before getting back in the water. In most cases this takes 12 to 24 hours,  not weeks, and it’s better to be safe than sorry!

How to remove Green Algae from your pool

Green algae is the one you’re most likely to come across. Thankfully, it’s also the easiest to deal with.

  1. Use a pool water test kit to check the overall health of the water, including chlorine and pH levels
  2. ‘Shock’ your pool with a purpose-built shock product (available at your local pool store). Follow the instructions on the label as the process and amounts will vary by product. Run your pool filter to make sure this product is circulating throughout the pool.
  3. The following day, check for any algae debris around your pool and clean it out if necessary.
  4. Use your test kit again to see how healthy your levels are after this treatment
  5. If your pH or chlorine levels still need adjusting, follow the appropriate instructions shown on the kit to get it back into a healthy range.

How to remove Yellow (Mustard) Algae from your pool

Since yellow algae attaches to the hard surfaces of your pool and is resistant to chlorine, there are a few extra steps required.

  1. Remove any toys and equipment from your pool and clean them thoroughly
  1. Run your pool filter and thoroughly scrub the floor and walls of your pool to physically remove the algae
  2. Use a pool water test kit to check the overall health of the water, including chlorine and pH levels
  3. ‘Shock’ your pool with a purpose-built shock product (available at your local pool store). Follow the instructions on the label as the process and amounts will vary by product. Run your pool filter to make sure this product is circulating throughout the pool.
  4. The following day, use your test kit again to see how healthy your levels are after this treatment
  5. If your pH or chlorine levels still need adjusting, follow the appropriate instructions shown on the kit to get it back into a healthy range.
  6. Now that your water is back to healthy levels and the visible algae has been removed, use an algaecide to kill any remaining levels in the water
  7. Use your test kit a final time to make sure levels are still happy and healthy before you start swimming.

How to remove Black Algae (aka Blue-Green Algae) from your pool

Black algae poses the most health risks and is also the most difficult to remove. Since it isn’t technically an algae, forms roots in porous surfaces and has a protective layer, regular levels of chlorine and algaecide alone aren’t going to cut it.

1. Remove any toys and equipment from your pool and clean them thoroughly

2. Run your pool filter and thoroughly scrub the floor and walls of your pool to physically remove the algae. You’ll need a heavier brush and a lot more elbow grease than usual to really get in there and move it.

3. For any stubborn areas, you can break a chlorine tablet in half and use that to scrub away at the remaining black spots with the broken edge. Don’t forget your chemical-resistant gloves and eye protection before handling these tablets.

4. Clean your pool filter thoroughly to make sure it doesn’t spread more of this ‘algae’ once you’re done cleaning

5. Use a pool water test kit to check the overall health of the water, including chlorine and pH levels

6. Now that you’ve removed the algae from its roots and broken down that protective layer, it’s time to give it a heavy shock with a purpose-built shock product (available at your local pool store).

Because we’re dealing with such a hardy adversary, this is a rare occasion where we recommend quadrupling the amount of pool shock you use. Submerge all of your pool cleaning equipment at the shallow end while you do this to remove any remaining algae there too.

7. Leave your pump to run for 24 hours to mix that pool shock throughout the pool and let it get to work. The water might be cloudy at this point. That’s normal and it will clear up.

8. While the pump is being left to run, it’s time to scrub all the hard surfaces of your pool again to remove any remaining algae that might still be attached, even if not visible. Remember, we’re dealing with a root system as well as the visible parts.

9. After your pump has been run for 24 hours, it’s time to give that filter a thorough cleaning again. By this point, any algae in there should have been destroyed but it’s not worth the risk.

10. Use your test kit again to see how healthy your levels are after this treatment

11. If your pH or chlorine levels still need adjusting, follow the appropriate instructions shown on the kit to get it back into a healthy range.

12. Over the next few days, keep a close eye on any areas that were affected by the black algae before. If you start to see anything visible, you’ll have to repeat the process again to get rid of it once and for all.

Common Questions about Pool Algae

Can I swim in my pool if it’s green with algae?

Although technically the answer may be yes, we would never recommend it. Not only is green water unappealing and often slimy, it can sustain life for other organisms that could pose a serious health risk.

Can I swim in my pool if there is yellow algae?

Just like green algae, yellow (mustard) algae itself isn’t inherently dangerous. Still, we don’t recommend swimming while the algae is present as it may be supporting harmful bacteria.

Can I swim in a pool with black algae?

No. Depending on the species, Black Algae (aka Blue-Green Algae) can bring a range of health hazards:

  • Swallowing water containing algae toxins may cause gastroenteritis symptoms such as vomiting, diarrhoea, fever and headache. The toxins produced by blue-green algae may also affect the liver, kidneys or brain.
  • Inhaling affected water may cause respiratory problems and flu-like symptoms.
  • Skin contact with water, including sensitive areas such as the eyes, ears, mouth and nose, may cause irritation, skin rash, flu-like symptoms, and fever.

Source: SEQ Water

How long does it take to get rid of algae in the pool?

Removing algae from your pool can take anywhere from 12 hours to several days. This depends on the type of algae you’re dealing with and how severe the problem