The Quickest Way to Kill Pool Algae
, by Tim Lyons, 6 min reading time
How to Get Rid of Algae in Your Pool (And Keep It From Coming Back)
How to Get Rid of Algae in Your Pool (And Keep It From Coming Back)
Nothing ruins a crystal-clear pool faster than algae. It starts small, but if left untreated, it multiplies quickly and can turn your pool into a murky green mess. Understanding what causes algae and how to treat it effectively can save you time, energy, and frustration throughout pool season.
What Causes Pool Algae?
Algae spores are everywhere — carried by wind, rain, or even contaminated swimwear and pool toys that have been in lakes, rivers, or oceans. On their own, spores aren’t a huge issue. The real problem begins when your pool’s water chemistry falls out of balance or filtration and circulation become inefficient. Low chlorine levels, unbalanced pH, and dirty filters create the ideal environment for algae to thrive.
Prevention is much easier than treatment. That’s why regular pool maintenance and water testing are crucial for avoiding algae outbreaks.
Types of Pool Algae (And How to Identify Them)
Before jumping into treatment, it’s important to recognize the type of algae you're dealing with:
1. Green Algae
The most common type — and the easiest to remove. It appears as cloudy water or green slime on your pool’s surfaces and spreads rapidly. It ranges from light green to dark green and can take over quickly if not addressed.
2. Yellow Algae (Mustard Algae)
A rarer form, this appears as yellow or brownish dust in shady areas of your pool. It’s chlorine-resistant and requires more aggressive treatment. It can resemble pollen, making it easy to overlook.
3. Black Algae
Technically a bacteria, black algae has strong root systems that burrow into concrete and plaster pool surfaces. It’s one of the toughest types to eliminate and often requires repeated, deep cleaning.
4. Pink Algae (Pink Slime)
Despite the name, this isn't algae at all — it’s an airborne bacteria. Found in corners, skimmers, and other low-flow areas, it looks like pink slime and requires a different treatment approach than green or black algae.
Step-by-Step Guide: How to Kill Pool Algae
If you’ve already spotted algae in your pool, don’t panic — but don’t wait either. Here's how to tackle it step by step:
1. Manually Vacuum the Pool
Use the “waste” setting on your filter to vacuum. This bypasses your filter system, preventing algae spores from circulating back into the water. Focus on areas with visible algae and maintain water levels while vacuuming.
2. Brush Pool Walls and Floor
Use a stiff pool brush to scrub all surfaces, especially shady corners, steps, and crevices. This helps dislodge algae and allows your sanitizer to work more effectively.
3. Test and Balance the Water
Before shocking the pool, test the pH and alkalinity. Balanced water allows chlorine to work at its full strength. Aim for a pH between 7.2–7.6 and alkalinity between 80–120 ppm.
4. Shock the Pool
Super-chlorinate the water to kill the algae. The dose depends on the type and severity of algae:
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Green Algae: Double dose
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Yellow Algae: Triple dose
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Black Algae: Quadruple dose
Shock at dusk or at night for best results — sunlight reduces chlorine’s effectiveness.
5. Run the Pool Filter
After shocking, run your filter continuously for at least 8–12 hours or overnight. Expect the water to become cloudy — that’s a sign the algae is dying and being filtered out.
6. Retest and Rebalance Water Chemistry
After filtration, test your water again. Make sure chlorine has returned to safe levels and adjust your pH, alkalinity, and other chemicals as needed. You may also want to check cyanuric acid and calcium hardness, especially if you added new water.
7. Clean the Filter Thoroughly
Your filter has just processed a lot of algae and bacteria. Backwash your sand or D.E. filter, or clean your cartridges well. A dirty filter can reintroduce algae spores back into the water if not cleaned properly.
Algaecide and Flocculants: Should You Use Them?
While not necessary for major cleanups, algaecide and flocculants can be helpful:
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Algaecide is best used preventively or after cleaning to kill lingering spores.
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Flocculant is effective for clumping together small particles (like early-stage algae), making it easier to vacuum them out. It’s a good option for mild, early infestations.
How to Prevent Algae From Coming Back
Algae prevention is all about consistency. Here are key maintenance tips:
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Test and balance water weekly, especially after heavy use or rainstorms
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Shock your pool weekly during warm weather or peak usage
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Run your pump 8–12 hours per day to ensure full circulation
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Clean your filter regularly and replace cartridges as needed
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Rinse swimsuits and pool toys used in natural water sources
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Add algaecide or flocculant as a preventive measure, especially in humid or high-risk climates
Frequently Asked Questions About Pool Algae
Can you swim in a pool with algae?
Technically, yes—but it’s not a good idea. Algae itself isn’t highly dangerous, but it often signals poor water quality. Algae-filled pools can harbor harmful bacteria like E. coli, and the cloudy water can make it hard to see the bottom, posing a safety risk for swimmers.
How do you treat algae in a saltwater pool?
The process is the same as with traditional chlorine pools. Even though saltwater pools generate chlorine differently, the treatment steps—brushing, vacuuming, shocking, and filtering—remain the same. Just be sure to monitor your salt system and water chemistry closely.
Does phosphate remover kill algae?
No. Phosphate removers cut off a food source that algae feed on, but they don’t kill algae directly. If your pool’s sanitizer levels (like chlorine) are where they should be, you generally don’t need to worry about phosphates. The best algae defense is clean, balanced water.
Does pool shock kill algae?
Yes—shock treatments are one of the most effective ways to kill algae. By raising chlorine levels quickly, shock destroys algae and other organic contaminants. Just remember to brush and vacuum your pool beforehand to help the shock work more efficiently. It’s normal for water to turn cloudy afterward; that’s dead algae being filtered out.