Algae is one of the most frustrating problems pool owners face. It turns sparkling water into an unsightly cloudy, green mess and can quickly take over your pool floor, surfaces, filters, and equipment.
Algae growth is often caused by poor water circulation, unbalanced chemical levels, and debris, such as leaves, that enter the pool. If you ever find yourself having to deal with green, yellow, or black algae, it is essential to act fast to protect your pool and keep it safe for swimming.
In this complete, step-by-step guide, we’ll walk you through exactly how to get rid of algae in pool water. And, more importantly, how to prevent it from coming back.
Key Takeaways
- Algae thrive in swimming pools with poor circulation, low chlorine levels, and unbalanced pH.
- Green algae is the most common, but yellow (mustard), black, and pink types also occur.
- When cleaning, brush the pool walls and floor thoroughly to loosen algae.
- Regularly test and balance your water chemistry, especially chlorine and pH levels.
- Shock your pool to kill algae spores, then run your pump for at least eight hours.
- Add algaecide and vacuum the pool to remove algae and debris.
- Regular brushing, filtration, water testing, and phosphate control help prevent algae growth from recurring.
- Fibreglass pools are less prone to algae due to their smooth surface.
- Call a pool professional if green pool water keeps returning or you have a black algae infestation.
What Is Pool Algae and Why Does It Grow?
Algae is a common issue that almost every pool owner in Australia will face at some point. It can turn clear pool water into a murky green mess and make surfaces slimy and unsafe.
For this reason, understanding what algae is, why it grows, and how it affects your pool is the first step towards keeping your water clean, healthy, and ready for swimming.
What Is Algae?
Algae are microscopic plant-like organisms that multiply rapidly in warm, nutrient-rich environments. In any swimming pool sizes, they can appear as green slime, yellow stains, or even black spots embedded in the surface.
Once they take hold, pool algae growth is very tough to eliminate without adding chemicals and proper treatment.
Why Do Pools Get Algae?
Algae spores enter the pool via wind, rainwater, dirt, and debris and they tend to bloom if it has poor filtration, low chlorine levels, and an unbalanced pH.
Algae feeds on nutrients like phosphates and stagnant water is a breeding ground for it, especially in warm weather.
How Algae Affects Your Pool
Typically, algae growth can be a real nuisance as it discolours pool water, creates slippery surfaces, and can clog your pool filter. In addition, it also reduces the water quality and makes your pool unsafe for swimming.
If left untreated, algae can damage pool surfaces and require costly maintenance to get rid of it.
Types of Pool Algae and How to Identify Them
Did you know? There are over 20,000 types of algae. However, when it comes to swimming pools four common types affect them.
These different types of pool algae have their own characteristics, levels of resistance to treatment, and appearances. So, knowing what you’re dealing with can help you choose the most effective way to treat and remove it.
Below are the four most prevalent types of algae you may encounter in your swimming pool.
Green Algae
Green algae is the most common type found in pools and can quickly coat surfaces with a slimy film. It grows quickly in warm, poorly circulated water and can turn your pool water cloudy or completely green, which can be quite off-putting.
The good news is green pool algae is also the easiest to treat with proper brushing, the use of pool chemicals, and decent filtration.
Yellow (Mustard) Algae
Yellow pool algae, or mustard algae, grows in shaded areas and is known for its resistance to chlorine. Pollen or dust can lead to yellow algae blooms in pools during humid conditions that form in shaded or hard-to-reach areas like pool corners or under pool toys.
Yellow algae requires multiple treatments to eliminate it due to its resistance to standard chlorination.
Black Algae
Of all the algae types, black pool algae is the most potentially damaging and stubborn form to get rid of. Also known as cyanobacteria, it can cause structural damage to pool surfaces if left untreated.
Black algae is difficult to remove due to its protective layer and strong roots that anchor to pool surfaces. As it thrives in poorly maintained pools, it requires a good few hours of aggressive brushing and strong chemicals that sit overnight to remove because it penetrates deep into the surface of concrete.
Pink Algae
Despite its name, pink algae is actually a type of bacteria that grows in pools with poor filtration and can appear as streaks or spots.
It usually manifests as pink or reddish slime, often around the waterline, ladders, or behind pool lights and is treated with antibacterial agents rather than standard algaecides.
Algae Colour and Severity: What It Means
In general, the darker or more widespread the algae, the more severe the infestation. For instance, a light green tint may be resolved with a quick shock treatment. However, dark green water or stubborn black spots often require professional help and deeper cleaning methods.
How to Get Rid of Pool Algae (Step-by-Step)
If your pool has turned green, cloudy, or slimy, don’t panic. With the right steps, you can get rid of pool algae and return your water to crystal clear.
Regardless of whether you’re dealing with green algae, mustard algae, or stubborn black algae, this step-by-step guide will help restore your swimming pool and prevent future outbreaks.
Step 1: Skim and Remove Debris
Start by removing all visible leaves, dirt, and how much debris is on the pool surface using a skimmer.
This type of organic matter provides nutrients that algae feed on, so getting rid of it early in the process is essential step to take. Don’t forget to remove pool toys and give them a clean, as they can carry algae spores too.
Step 2: Brush Pool Walls and Floor
Use a stiff pool brush to scrub all surfaces thoroughly, including pool walls, steps, ladders, and the floor. Brushing them helps to break up the algae and expose it to sanitising chemicals.
If you have a fibreglass pool, its smooth surface makes this process much easier, although brushing it is still necessary.
Step 3: Check and Adjust Water Chemistry
You should regularly test your pool water using a test kit or strips. The ideal levels to aim for are:
- Chlorine: 2–4 ppm
- pH: 7.2–7.6
- Alkalinity: 80–120 ppm
Unbalanced water can make chlorine less effective. So, if you notice that phosphate levels are high, use a phosphate remover, because algae thrives on nutrients like phosphates.
Step 4: Shock the Pool With Chlorine
Shock treatment is recommended weekly to help maintain water clarity and kill bacteria, algae spores, and other contaminants.
If you are experiencing a more severe infestation or resistant algae (like mustard or black), don’t be afraid to use a double or triple dose. Just make sure you keep the pool pump running for at least eight hours to circulate the chlorine.
Step 5: Run Pump Continuously and Clean Filter
Running your filtration system every day helps to maintain a good level of pool cleanliness. In addition, you should also backwash or clean your pool filter (or replace filter cartridges) to remove dead algae.
If left unchecked, algae can clog filters, reduce circulation, and undo all your hard work. For this reason, vacuuming the pool at least once a week is also a good idea to keep it clear of debris.
You should also consider running a minimum of two complete turnovers of pool water every day to maintain for good circulation.
Optional: Use Flocculant or Algaecide for Stubborn Algae
If the water remains cloudy or you’re still seeing algae, consider adding a pool algaecide or flocculant.
Algaecide helps kill any remaining algae, while flocculant binds particles together so they can be vacuumed out. Use these products as directed and only when needed.
Floc vs. Algaecide: Which One to Use and When?
When you’re battling pool algae, two common chemical treatments often come up: flocculant (or “floc”) and algaecide. But while both can help clear up murky or algae-ridden water, they serve different purposes.
For this reason, understanding when and how to use each can save you a lot of time, money, and unnecessary frustration.
What is Flocculant?
Flocculant is a chemical that binds together fine particles, including dead algae, dirt, and other contaminants, and sinks them to the bottom of the pool. This process is called “floccing.”
Once settled, the debris can be removed manually with a vacuum. Floc is ideal when your water remains cloudy even after brushing and shocking.
What is Algaecide?
Algaecide is a targeted treatment designed to kill algae or prevent it from growing. Different formulas are made for green, yellow, or black algae.
Algaecide works best as a supporting chemical after shocking the pool or as part of a regular maintenance routine to prevent algae blooms before they start.
When to Use Each (or Both)
You should use algaecide when algae is actively growing or if your pool is prone to recurring blooms. By contrast, flocculant is best when your water stays cloudy or has suspended particles after treatment.
That said, in the most stubborn cases of pool algae, both may be used. Shock first, then algaecide, and finally, floc to remove what’s left.
Mistakes to Avoid
When you treat pool algae there are some easy mistakes you can make. With that in mind:
- Don’t use floc in pools with cartridge filters as it can clog them.
- Avoid overdosing on algaecide. Too much can cause foaming.
- Never add both products at the same time unless directed. Doing this can reduce their effectiveness at getting rid of pool algae.
- Always run your pool pump and brush thoroughly before adding either product.
How Long Does It Take to Kill Algae?
Getting rid of algae in your pool can take time and will depend on the type of pool algae you are experiencing, how severe the infestation is, and whether your treatment steps are effective.
Here’s what to expect when tackling algae problems.
Typical Timelines by Algae Type
- Green algae often clear up within 24 to 48 hours after a proper pool shock, brushing, and filtration.
- Yellow (mustard) algae may take several days and often needs multiple shock treatments and brushing.
- Black algae is the most stubborn and can take a week or more with strong pool chlorine chemicals and repeated scrubbing to fully remove it.
What If It Doesn’t Clear After 48 Hours?
If your pool water still looks green or cloudy after two days don’t panic. Check your chlorine levels, brush again, manually vacuum any free-floating debris (even if its small) and clean or backwash your filter.
You may also need a second round of shock treatment, or to use a specialised algaecide or flocculant to finish the job. If that doesn’t work, then call in a professional.
How to Prevent Pool Algae From Coming Back
Once you’ve cleared your pool of common algae, the last thing you want is for it to return. The good news is that algae prevention is far easier than algae removal.
With consistent care, get water balance and a few savvy habits, you can keep your pool water clear and healthy all year round. Here’s how to prevent algae from making an unwanted comeback.
Maintain Proper Chlorine & pH Levels
As algae thrives in unbalanced pool water, you should keep your chlorine levels between 2 and 4 ppm and maintain a pH between 7.2 and 7.6.
It is also a good idea to test your pool water at least twice a week, especially in summer or after heavy use. The more balanced water you have, the more it helps your sanitiser work effectively to kill algae spores before they grow.
Keep Pool Clean and Circulating
Algae loves still water. So, make sure your pool pump runs for at least eight hours per day to allow full circulation. Clean skimmer baskets and remove debris regularly and use carbon dioxide treatments as necessary.
Regular Brushing and Filtration Maintenance
Brush your pool walls, steps, and floor on a weekly basis to prevent algae from attaching to surfaces. You should also clean your pool filter regularly and backwash when needed to maintain strong circulation.
Don’t forget to check your pressure gauge, a spike may indicate a clogged filter. When not using it, always put a pool cover over the surface water.
Seasonal Algaecide Use
Adding an algaecide during warmer months or when closing the pool for winter can offer extra protection. It is a good idea to use a preventative dose rather than a treatment dose to maintain clarity and stop new algae from taking hold.
Post-Rain Pool Care
Rain can introduce algae spores, phosphates, and debris into your pool. After heavy rain, test your water and rebalance chemicals. Also consider running your filtration system longer and shock the pool if needed to stop algae before it starts growing.
