The Ultimate Guide to Eliminating Pool Algae

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poolquip

March 14, 2025

On August 26, 2021

Why Does Algae Appear in Pools?

Algae in your pool is more than just an eyesore; it’s a sign of imbalanced water chemistry. It typically forms due to low chlorine levels, inadequate filtration, or improper water balance. Additionally, it can enter your pool through swimwear or pool accessories previously used in natural water sources like lakes or rivers.

If you catch it early, you can stop algae before it takes over. However, if ignored, it will rapidly spread and turn your pool into a murky mess.

Unfortunately, simply adding standard amounts of chlorine or running the pool filter won’t be enough to kill algae spores effectively.

Common Causes of Pool Algae

Algae spores exist everywhere—in the air, rain, and dirt. These tiny particles can easily make their way into your pool. However, the real problem begins when they start multiplying due to poor pool maintenance. Here are the key factors that encourage algae growth:

Low chlorine levels – Not enough sanitizer allows algae to thrive.
Unbalanced pH – High or unstable pH levels create an ideal environment for algae.
Dirty filters – Clogged filters reduce water circulation, making it easier for algae to settle.
Poor circulation – Stagnant water allows algae to attach and spread.
Contaminated swim gear – Toys, floats, and swimsuits that have been in natural water can introduce algae to your pool.

Prevention is Key

It’s far easier to prevent algae than to eliminate a full-scale bloom. To keep your pool clear:

Maintain proper water chemistry by checking pH and chlorine levels regularly.
Keep your filter system clean and running efficiently.
Rinse off any swimsuits and pool accessories before using them in your pool.

The Ultimate Guide to Eliminating Pool Algae

Types of Pool Algae and How to Treat Them

Identifying the type of algae in your pool is the first step to getting rid of it. Below are the most common types and the best ways to tackle them.

1. Green Algae

Green algae is the most common type and can be seen floating in water or clinging to pool walls and floors. It often results from poor sanitation and filtration. When left untreated, it can turn your pool water cloudy or green.

How to Get Rid of Green Algae

Brush the pool walls and floor daily.
Increase chlorine levels by turning up your chlorinator.
Use an algaecide and follow up with a shock treatment.

2. Mustard Algae (Yellow Algae)

This type of algae is chlorine-resistant and has a yellow or tan appearance, often mistaken for dirt or sand. It typically grows in shaded areas of the pool and is more stubborn than green algae.

How to Get Rid of Mustard Algae

Brush the affected areas daily.
Vacuum the pool using the "Waste" setting to bypass the filter.
Shock the pool with double the recommended amount of chlorine.
Apply a strong algaecide.

3. Black Algae

Black algae is the toughest to eliminate. It appears as small black spots on pool surfaces, especially in porous materials like concrete and gunite. It has deep roots that make it resistant to chlorine and brushing.

How to Get Rid of Black Algae

Clean and backwash your pool filter.
Brush pool walls and floors aggressively with a stainless-steel bristle brush.
Apply a high-dose chlorine shock.
Use a heavy-duty algaecide.

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Quick & Effective Steps to Kill Pool Algae

Step 1: Manually Vacuum Your Pool

Automatic pool cleaners aren’t ideal for removing algae. Instead, manually vacuum your pool using the "Waste" setting on your filter to prevent the contaminated water from circulating back.

Pay extra attention to algae-heavy areas. Also, ensure you maintain the water level by refilling as needed during vacuuming.

Step 2: Brush Pool Surfaces

Scrubbing algae off pool walls and floors helps chlorine penetrate deeper, making it more effective in killing the spores. Use a stiff-bristle pool brush attached to a pole, focusing on corners, steps, and shady spots where algae thrive.

For concrete or gunite pools, use a brush with stainless-steel bristles. For vinyl and fiberglass pools, opt for a softer nylon-bristle brush to avoid damage.

Step 3: Test and Balance Water Chemistry

Using test strips or a liquid test kit, check and adjust the pH, alkalinity, and chlorine levels. Properly balanced water ensures your sanitizer is fully effective against algae.

pH should be between 7.2 and 7.6
Chlorine should be around 3-5 ppm
Alkalinity should be between 80-120 ppm

Step 4: Shock Your Pool

A high dose of chlorine shock is necessary to kill off remaining algae spores. Follow these tips for best results:

Use calcium hypochlorite shock for green algae.
Apply double or triple shock for mustard or black algae.
Shock the pool at night to prevent sunlight from breaking down chlorine too quickly.

Step 5: Circulate and Filter

Run your pool pump continuously for at least 24-48 hours after shocking. This ensures that the chlorine spreads evenly and the filter catches dead algae particles. Clean or backwash the filter frequently during this process.