Algae In Swimming Pools – How To Get Rid Of It Fast and Forever!

Pool algae may seem quite innocuous at first. After all, what’s wrong with a bit of weed growing in the water? It’s the most natural thing in the world…except, it’s gross..

While it’s true that green algae does not cause any harm to humans, the bacteria that feed on the algae can pose a health risk. Give algae a chance to thrive and it will balloon into an ugly problem that can be both difficult and expensive to fix.


Algae can damage motor, pumps, filters, grains and totally ruin a pool if left unchecked! It results in poor underwater visibility. Even worse, this slimy substance causes pool surfaces to become slippery and can lead to accidents.

Algae is also an indication that your pool chemistry is out of whack. Basically, this means that along with algae, a host of other potentially harmful micro-organisms are having a ball of time in your pool!

The color green looks good on dollar bills, not in your swimming pool. So let’s find out what causes algae in pool, what are the different types of algae and how to get rid of pool algae – fast and forever.

Symptoms of Pool Algae:

Most of the time, algae makes its presence known by imparting a greenish tinge to the water. The water might also take upon a yellowish or blue-black color depending upon the type of algae that’s present in it.

The water becomes cloudy and if the growth is not controlled, visibility becomes so poor that you may struggle to see the bottom of the pool.

Algae likes to hide in nooks, crannies and hard to spot places. It usually grows in corners, around steps and close to jets and skimmers.

Algae spores enter the pool all the time. They are brought in by the wind, rain, contaminated swimsuits and pool cleaning tools etc. If your water chemistry is not right, the spores will thank you for your hospitality and bloom in a mater of hours.

You can wash swimsuits and tools before using them in the pool. Still, you cannot control factors such as humidity, sunlight, wind etc.

So you can be 100% sure that algae spores will gain entry into your pool, one way or the other. You have to be ready to tackle the problem before it gets out of hand.

Types of Pool Algae:

Often, the exact tint of the water may not be so obvious. The fact that the water becomes cloudy makes it even harder to identify the color.

So, in order to find out what type of algae has taken up residence in your pool, you’ll have to take a closer look at the spots where it has started to grow.

Green Algae:

This type of algae is known as Chlorophyta; it gets its name from chlorophyll, which is also responsible for the green color. Green algae floats in water and also attaches onto walls and floor.

Swimwear and toys that have been used in natural bodies of water and then reused in the pool without sanitizing cause green algae to enter pool water.

Inefficient filtration and lack of proper sanitization can boost growth of green algae. This type of algae is the most common and thankfully, it is the easiest to kill.

Yellow Algae:

Also known as brown or mustard algae, yellow algae looks like pollen or sand. It is much rarer than green algae and unlike the latter, it is not slimy. It is resistant to chlorine which makes it hard to get rid of.

Black Algae:

The scientific name for this type of algae is cyanobacteria. Thus, technically, it’s not even algae but it is extremely potent due to the fact that it can make its own food.

It’s like a monster that just doesn’t stop growing and what’s more, its roots can penetrate into concrete. Hence, it is extremely hard to eradicate.

(Please note that pink slime, which is actually a type of bacteria and often wrongly called pink algae, can also be found in pools, especially in PVC pipes.

Pink slime does not harm humans but it can harm the pool. It is extremely resistant to cleaning agents and chemicals, including chlorine.)

How To Get Rid Of Pool Algae:

Step 1 - Vacuum the pool:

Many pool experts opine that manual vacuuming is the best solution for pool cleaners. However, this is an extremely labor-intensive exercise that can take up a lot of time depending upon the size of your pool.

So unless you want to recruit kids, their friends and their friends’ friends to help you with cleaning the pool, this might not be the ideal option for you.

Manual vacuuming also requires quite a bit of DIY, so it might be more practical to stick to robotic pool cleaners.

Please ensure that you don’t just rinse the filters after using robotic pool cleaners in a pool that is infested with algae.

Some spores may get trapped into the filters and will be reintroduced into the water the next time you use the pool cleaner. Give the filters a thorough wash with detergent/soap.

Step 2 – Brush like there’s no tomorrow:

You will need a stiff pool brush for this purpose.

Most pool cleaners cannot handle corners and steps well and hence you have no option but to manually brush the walls, corners, steps and floor extremely well.

This will help to loosen the algae and increase the efficacy of pool sanitizer. Use long strokes and make sure to overlap your strokes so that you do not miss out on any key areas. 

Note that the water will become cloudier as you go and affect visibility. So get to the problem areas first.

Step 3 – Test & Balance Pool Water: 

This is easier said than done but there’s simply no way around it. So you’ll have to fight your way through all the jargon and test the chemistry of your water.

You can do this with the help of strips, digital kits, liquid kits etc. They all come with instructions so follow them to the dot.

Please note that we are trying to determine the chlorine levels, pH and alkalinity of the water.

We will then adjust these parameters so that they’re within the recommended range.

This basically prepares the pool for shocking. If these levels are unbalanced, shocking is less effective.

Step 4 – Shock the pool:

While conventional wisdom suggests using stabilized chlorine to shock the pool, it causes too much cyanuric acid, which diminishes the effects of sanitizer. So it is much better to use calcium hypochlorite

Read the package instructions for the recommended dose for your pool size. Then multiple that dose by 2 for green algae, 3 for yellow and 4 for black algae.

Throw cleaning tools into the pool while shocking. It sanitizes them thoroughly.

Step 5 – Filter out dead algae and Test Again:

After shocking, the water will look cloudy blue. Turn on pool filter for at least 8 hours. (Then sanitize or replace the filter itself) You can use pool water clarifier to speed up the process.

Once done, check pool chemistry meticulously (using a kit) before entering the water. pH, chlorine and alkalinity levels should be within the normal range.

Flocculant and Algaecide: These also help in getting rid of algae however they both have their limitations.

Flocculant works only for small amounts of green algae. It basically binds to the algae so that it can be filtered out of the pool.

Algaecide does kill algae, but it works better as a preventive measure. Once pool has been shocked, wait for the chlorine levels to drop below 5 parts per million and add algaecide (refer package instructions to determine dosage). Give pool surfaces a good brushing to loosen up the algae. Once dead, the algae will be filtered out.

Remember, algae can also infest salt water pools. Cleaning instructions remain the same. Please don’t forget to use calcium hypochlorite (the pool shock treatment I mentioned above).

Adopt a three pronged approach to prevent re-occurrences of algae in pool:

Our website has lots of detailed info on pool cleaning, robotic pool cleaners and maintenance

Some pool cleaners can climb walls while others cant. If you get one that cannot climb walls, you’ll have to scrub them yourself. Some can do walls but struggle with stairs.

So please DO NOT buy a pool cleaning bot unless you’ve read our reviews! You’ll thank us later.

We did the research for you, and recommend the #1 Top Rated Automatic Pool Cleaner on - the Dolphin Nautilus CC Plus:

BUT - If your pool tends to collect a lot of debris (leaves, bugs, etc) on top of the water, we'd suggest going with a pressure side cleaner such as the Polaris 360.  

The Polaris 360 not only cleans the bottom of your pool, but it uses your pools return water to create a suction vortex which essentially pulls junk from your swimming pool into the bag attached to the top of the device.

Unlike many pressure side cleaners, a booster pump is NOT required to use it, as it uses your swimming pools circulation pump!

Check out the Polaris 360 on Amazon, here.

Enjoy your algae-free pool! 

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