Pool Algaecide: How To Get Rid Of Pool Algae Fast

Algae blooms sometimes seem to happen overnight. One day, you’ve got a beautifully clean pool, the next, some discolouration and cloudiness, and soon after you’ve got a full algae bloom. 

Algae is a frustrating, annoying problem for any pool owner, and eliminating it from your pool system is sometimes difficult. So how do you get rid of algae when it’s blooming, and how do you prevent algae blooms from happening? 

Well, you’re about to find out!

In this article, we’ll cover:

  • What causes algae in pools
  • How to get rid of algae fast
  • Pool algaecide

Let’s dive in.

What Causes Algae in Pools?

At a microscopic size, algae are always present in swimming pools. Algae can cause problems when it blooms, or multiplies when the conditions are right for growth. 

Things that promote algal growth:

  • Low or poor water circulation creating dead spots in the pool
  • Low or inconsistent chlorine levels
  • An ineffective filter or short filter run times
  • Imbalanced water with pH, alkalinity, calcium or cyanuric levels that are off

Algae needs nutrients to grow. When your chlorine levels are low and the pH is high, or if your pump and/or filter aren’t working at optimal capacity, that microscopic algae that’s always present in your pool may seize the opportunity to grow out of control.

How do algae get in my pool?

Algae can arrive in your pool in any number of ways. 

It can be introduced into your pool by being present on pool toys, accessories, or even on swimwear – especially if they’ve been used or worn in the ocean. Algal spores can also be blown into your pool on a speck of dirt, or arrive with rainwater runoff.

Not cleaning or replacing your pool filter after a previous algae bloom, or not using the right amount of chemicals to shock your pool can also be the cause of another algae bloom. 

Circulation, water balance, sanitation and filtration all need to be working at their best to prevent algae blooms from occurring and recurring.

 Algae isn’t just a chlorine pool problem: saltwater pools experience algae blooms too.

Is it harmful to swim with algae in the pool?

Algae isn’t directly harmful to swimmers, although it can be unpleasant to swim in a cloudy, oddly coloured pool. It can also be dangerous to perform rescues or dive in an algae infested pool because swimmers’ field of vision is restricted by cloudy waters.

What can be harmful is pathogenic bacteria like E.Coli that feed on algae. So if you’re experiencing an algae bloom, the safest, and cheapest option is to deal with the problem as quickly as possible.

Types of algae in pools

Here’s an overview of the types of algae you’ll find in pools.

Green Algae
Green algae in a swimming pool

Green algae is one of the most common varieties that pool owners see. It can be found free-floating in the water or clinging to pool walls. Don’t confuse green algae with severe copper precipitation which creates clear green water – green algae makes your pool water cloudy. Some green algae can appear as spots on surfaces or rough areas, especially in areas of your pool where circulation is low.

Mustard Algae
Mustard algae in a swimming pool

Mustard algae are sheet forming and are usually found in shady areas of your pool. It can be difficult to eradicate, because it’s generally resistant to normal chlorine levels and can survive algaecide treatment on pool toys, cleaning equipment, swimsuits, or even within the pool filter.

Black Algae
Black algae in a swimming pool

Black algae, also known as ‘blackspots’ are extremely difficult to completely remove because of their strong roots and resistance to normal levels of sanitisation. 

It’s usually black or dark blue/green, ranging in size from that of a pencil eraser to a dollar. The roots of black algae grow into pool plaster or tile grout, and unless the roots are destroyed, new algae will form in the same place.

Pink Slime
Pink slime in a swimming pool

Pink slime is a bacteria that can plague your pool in much the same way as algae. It can be found on smooth surfaces in areas of low flow or circulation at the waterline, on light fixtures and pipe fittings. It thrives when chlorine levels are low or suppressed with high levels of cyanuric acid. 

Like mustard and black algae, pink slime requires a high level of chlorine to treat effectively and ensure it doesn’t come back. Pink slime is hazardous to swimmers, and you should treat your pool for it immediately. Thankfully, it’s pretty rare!

How To Get Rid of Algae Fast

If your pool is experiencing a small number of algae, try treating it with pool algaecide. If the algae doesn’t clear up, or returns soon after the algaecide treatment, try the more aggressive approach of shocking your pool. 

No matter what type of algae you’re trying to rid your pool of, when you have an algal bloom a shock treatment is recommended. There are a few steps you should follow to ensure you clear ALL algae out of your pool, preventing future blooms from occurring.

Step 1: Vacuum

Robotic and automatic pool cleaners aren’t well suited for cleaning up algae blooms, so the first step is to vacuum your pool manually

If the pool is resembling a swamp rather than a tropical oasis, then bypass your filter to prevent recirculation of contaminated water, sending the water directly to waste. Make sure you pay special attention to areas where algae are on the walls or floor. You will need to top the pool up as vacuuming the waste will drain the pool quite quickly. 

Make sure that the filter Multi-port valve is set to Waste, you should never vacuum to backwash.

If the pool only has a light infestation of algae then you could skip to the next step.820

Step 2: Brush

Use a stiff brush on a pole to scrub off any algae on the walls and floor, paying close attention to large algae deposits, corners and shady areas. Brushing allows sanitiser or ‘shock’ to permeate deeper into any algae left on the walls or floor. It’s easier for the shock and algaecide to work on the algae if it’s in suspension in the water rather than if it’s clinging to the walls.

TIP: Brush tough areas first. Brushing will stir up sediment and make the water of your pool cloudy. The more algae you dislodge, the more obstructed your view will become.

Step 3: Test and adjust

Test and balance your pool water. High pH or low alkalinity will inhibit pool shock. Adjusting your levels before shocking your pool ensures that the sanitiser will be effective against algae. 

If the amount of algae in the pool is extreme (e.g: you cant see the lights on the wall of the pool through the water), you may need to floc the pool later in the process. If so, it’s probably better to test and dose just the pH, and check the cyanuric acid levels are OK. 

This is because when you vacuum the waste to remove the floc, you will need to add more fresh water to the pool which will mean the pool will require balancing again.

If it’s only a light dose of algae, then do a complete balance of the pool.

Step 4: Shock and Dose

A shock treatment means creating a harsh environment to kill any algae or bacteria living in your pool. If the algal infection of your pool is heavy, you’ll need aggressive treatment to completely clear your pool and ensure that the algae don’t come back.

TIP: Shock your pool at dusk or night. If you shock your pool during the day the sun will degrade added chlorine before it’s had a chance to kill the algae.  

You should also add algaecide at this stage. There’s different algaecides for different algae types – let your pool shop advise you on which algae type you have and they will supply you with the right type to get the best results.

Step 5: Filter

Run your filter for a minimum of 8 hours, until the water clears – the shock treatment and algaecides used should turn your pool a cloudy blue. 

The longer the filter runs the better. If the pump noise doesn’t bother anyone, run the pump and filter 24 hours a day.

TIP: Add a clarifier to speed the process up.

You may need to backwash the filter quite often, sometimes daily until the water’s crystal clear again.

Step 6: Test (again)

You want to be sure your chemistry is balanced and your chlorine levels are back within normal range before anyone gets back into the pool. 

TIP: A Preventative Pool algaecide addition at this stage will help prevent future algae blooms

Depending on your pool and the type of algae you have, you may need to repeat steps 4-6 several times to kill the algae. Only when there is no trace of green left in the pool, should you go to step 7. What you are looking for is the pool to go from green to blue or cloudy blue/white.

When algae dies, the chlorophyll (which makes the algae green or coloured) leaches out and you’re left with white/grey dead algae floating in the pool. Once the algae is dead, your filter can easily trap it and you can backwash it away. 

Live algae will pass through the filter and return to the pool, so if you see a green jet of water coming out of your returns when vacuuming, you’ve still got live algae in the pool.

Step 7: Clean your pool filter

Backwash your filter again and give it a good deep clean. A deep clean of your filter is highly recommended after you’ve experienced an algal bloom to prevent any residual algae that have made it into your filter from finding their way back into your pool. 

Focus Filter Cleaner & Degreaser is a great product to use now.

Step 8: Enjoy!

Go for a swim in your algae-free pool!

Now that you know one of the ways to get rid of algae once you’ve experienced a bloom, let’s talk about how to prevent an algal bloom from happening in the first place.

Pool Algaecide

Most algaecide is best used as a preventative against algal blooms, not to solve the problem of a full-blown, large-scale algae problem. 

If you’ve been plagued by multiple algae blooms in a season, and you can’t seem to get ahead of the problem, you may need a different approach. Removing phosphates with Focus Banish Phosphate takes algae’s main food source out of the equation and may be the solution you need for tackling algae in your pool.

When to add algaecide to a pool

There are many different kinds of pool algaecide available on the market. Some can be used to combat algae blooms like Focus Hydroclear, and some like Focus Powercide 4 help prevent algal blooms from occurring in the first place, as well as treating some algae types. 

Tablets like Focus Multi Tabs can help balance chlorine, algaecide and clarification additions in an easy 3 in 1 step. 

After a shock treatment, wait for the chlorine levels to reduce to below 5ppm then add a dose of algaecide, following the instructions on the packaging. 

In tandem with your normal sanitation system, algaecide works best at preventing algae blooms from occurring when added regularly as a part of your sanitiser additions.

When to use flocculant

Flocculant is a type of clarifier and can be used as a small-scale algae combatant. It causes particles to clump together and fall to the bottom of your pool, making for easy vacuuming.

Flocculant is best for when you have a lot of algae in your pool or when you need to clarify the water quickly – otherwise we recommend that you run a clarifier in your pool. Focus Bling Tablets are an easy addition to your skimmer basket to keep your water sparkling year round.

Get Pool Algae Under Control

Algae is always present in your pool – it’s something that all pool owners have to contend with. 

But it doesn’t have to be something you battle on a shock treatment scale. 

Simple things that you can to control algae in your pool: 

  • Clean and sanitize all pool equipment, especially if it’s been used to combat an algae bloom.

TIP: Sanitise your pool tools by keeping them in the shallow end of your pool when you run a shock treatment.

  • Clean and sanitize all pool toys, and floats. Use a cleaner containing bleach or a diluted bleach solution.
  • Wash all swimwear, especially if it’s been worn in a lake, pond, or the ocean before going for a swim in your pool.
  • Maintain balanced pool chemistry. Run your pump 8-12 hours a day during the swimming season and shock when you need to. 
  • If your pool needs resurfacing, don’t wait. Pool surfaces with cracks or that are worn with age make the perfect hiding place for algae.

Pool Algae FAQs

Does chlorine kill algae in a pool?

Yes, and no. Normal levels of chlorine often keep algal blooms in check, but when the chlorine levels are low or there have been infrequent additions, an algal bloom can happen. 

Shocking your pool adds a large amount of chlorine to your pool in a single time that helps to kill algae.

How much algaecide do I put in my pool?

Always follow the instructions on the packaging. 

Calculate the volume of your pool, and decide if you’re performing regular algae maintenance or shocking your pool. If in doubt, ask your local pool shop how much and how often to add algaecide to your pool to prevent algae blooms.

How long does it take for algaecide to work?

It depends on the type and potency of pool algaecide you’re using. Running your pump allows the algaecide to circulate throughout your pool, clearing the water in a few hours. 

TIP: Allow the algaecide to circulate for 30 minutes to an hour before going for a swim otherwise you may limit the effectiveness.

About the author
Adrian Hill
Adrian Hill

Hey! I'm Adrian, founder and pool expert here at Dolphin Pacific. I love spending time with family, fishing, and have been known to brew my own beer.

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