How Long Does It Take Algae to Grow in Pool

logo by Editorial Staff | Posted on December 23rd, 2022

Are you wondering how long it takes for algae to take over your pool? Don’t worry; we’ve got the answers!

In this blog post, we’ll walk you through how long algae takes to grow in a pool and what you can do to prevent it. Read on to learn more about keeping your pool clean and clear!

A backyard pool with algae making the water green.

What is Algae, and where does it come from?

Algae is a microscopic aquatic organism that can exist in salt and fresh water. It is naturally present in most bodies of water and can vary in color from green to yellow, blue, and black.

Algae are also one of the most common forms of phytoplankton. These organisms can convert energy from the sun into food, meaning they can grow quickly if conditions are right.

Algae has become a prominent issue in swimming pools because it can quickly spread, resulting in an unsightly appearance and poor water quality.

How do algae grow in a pool?

Algae can grow in a pool quickly, especially in warm, sunny conditions. When the water is still, the algae take in sunlight and use photosynthesis to grow. Algae spores usually spread very rapidly and can take over a pool in a short amount of time.

A lack of proper sanitation, filtration, and high pH levels often cause this. Swimmers also contribute to the spread of algae by bringing elements like dirt, bacteria, and sunscreen into the pool.

The presence of organic matter from swimmers, such as dirt, bacteria, and sunscreen, can further accelerate the growth of the algae.

Algae usually grow on the walls, floors, and steps of pools but can also grow inside pipes and on decks. It’s important to treat algae as soon as possible to avoid a full-blown infestation.

Different Types of Pool Algae

Different types of algae can grow in a pool, each with its characteristics.

Green algae is the most common algae found in pools, but other types include black algae, blue-green algae, and diatoms.

  • Green algae typically grow quickly and multiply rapidly on warm, sunny days. It is usually found on the walls and floors of the pool or floating in the water.
  • Black algae are often found growing on the sides and bottom of the pool and are more difficult to remove than other types due to their strong root system.
  • Blue-green alga is a toxic alga that can cause skin irritations, respiratory problems, and other health issues.
  • Diatoms are single-celled organisms that look like sand in the water and can cause cloudy or murky water.
Cloudy green water in a outdoor inground pool.

Signs of Algae Growth in Your Pool

Algae growth in a pool is often obvious and easy to spot. You may notice a green or black discoloration on your pool’s walls, floor, or steps and a slimy film on the water’s surface.

Algae can also float in the water and form large clumps that are easily visible. You may also see debris or dead leaves that the skimmer has not filtered out. If you notice any of these signs, it’s time to take action and treat the algae growth in your pool.

How to Prevent Algae Growth in Your Pool

Preventing algae growth in your pool is key to maintaining a safe and healthy swimming environment for your family. Here are some tips on how to protect your pool from algae:

  1. Keep the pH level of your pool water between 7.2 and 7.6. This is the ideal range for preventing algae growth in pools.
  2. Keep the chlorine levels in your pool between 1 and 3 parts per million (ppm).
  3. Clean your pool regularly and vacuum the floor and walls to ensure that no dirt or debris has accumulated in the pool.
  4. Install an automatic pool cleaner, which helps to remove debris and dirt that can cause algae growth.
  5. Keep the pool filter clean and make sure it is functioning properly at all times.
  6. Cover the pool when it is not used to prevent dirt, leaves, and other debris from entering the water.
  7. Shock your pool with chlorine every week to prevent bacteria and other pollutants from accumulating.
  8. Check your pool’s water chemistry weekly and adjust it as needed.
  9. Regularly test the water for pH, alkalinity, calcium hardness, cyanuric acid, chlorine, and bromine levels.
  10. Use a clarifier once a month to help keep the water crystal clear, which also helps to prevent algae growth.

Chemical Treatments for Killing and Controlling Algae

Chemical treatments are one of the most popular methods for killing and controlling algae in pools.

Chlorine is the most common chemical used to treat algae, as it works quickly to kill off the algae and prevent its spread. Chlorine tablets can be a good choice for killing off existing algae, while chlorine shock treatments can be used to prevent future algae growth.

Other chemicals, such as algaecides and phosphate removers, can be combined with chlorine to help keep the pool free of algae.

It is important to note that these treatments should only be used with caution, as they can cause damage to your pool if used incorrectly. Additionally, regular testing of pool water is necessary to ensure that the right chemical balance is maintained.

Dirty swimming pool water

Physical Cleaning Methods for Removing Existing Algae

Physical cleaning is an effective way to remove existing algae from your pool. Vacuuming and brushing are two common methods used to remove algae from pool surfaces.

Vacuuming removes algae from the pool’s surfaces, while brushing removes it from the walls and floor.

To ensure thorough cleaning, it’s important to brush the entire pool in a circular motion, starting from the shallow end and working your way down.

This will help break up any clumps of algae and make them easier to vacuum out. Also, cleaning the filter regularly can help reduce the spread of algae in your pool.

Proper Maintenance Practices for Keeping an Algal-Free Pool

Proper maintenance is the key to keeping your pool free of algae. Regular testing and balancing your pool’s water chemistry are essential in preventing algae growth.

Check the pH, total alkalinity, and calcium hardness levels at least once a week. Also, make sure to clean the pool filter regularly. If you have a sand filter, you should backwash it at least once a month.

When testing your pool’s water, it is important to check for pH levels, alkalinity, calcium hardness, free chlorine, total chlorine, and cyanuric acid.

The ideal pH levels for pool water should range from 7.4 to 7.6, with an alkalinity level between 80 and 120 ppm. Calcium hardness should be between 200 and 400 ppm, and free chlorine should be 1 ppm.

For other filters, such as cartridges, diatomaceous earth, or DE filters, you should clean them according to the manufacturer’s instructions.

In addition, you should always keep the free chlorine levels between 1 and 4 ppm for optimal performance.

Finally, don’t forget to check and clean your pool skimmers and pumps often to remove dirt, debris, and other contaminants that can cause algae blooms.


In conclusion, algae can grow quickly in a pool if the conditions are right. Warm weather, sunlight, high pH levels, and lack of proper sanitation and filtration can all contribute to an algal bloom.

Different types of pool algae require different methods of removal and treatment. The most effective way to prevent algae growth is to maintain good pool hygiene and water chemistry and regularly test the quality of your pool water.

Chemical treatments, physical cleaning methods, and natural solutions are all effective ways to kill and control algae growth in your pool. With the right maintenance practices and proper sanitation, you can keep your pool algae-free for a long time.


Editorial Staff

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