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Prevent and Treat Algae

Swimming pools are a lot of fun but occasionally develop water problems, such as algae. Here are instructions on how to prevent, treat and remove pool algae.

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Introduction

Algae are microscopic plants that enter your pool by rain, wind and fill water. If allowed to grow unchecked, your water will quickly become unusable. Algae prevention and treatment is vital to effective and efficient pool care.

Causes of Algae Growth

Causes and Symptoms of Algae Growth

Algae growth is usually caused by one of the following conditions:

Inadequate, Free, Available Chlorine Levels
Free, available chlorine levels can be depleted quickly by heavy rains, high-bather loads or poor maintenance procedures. Check free, available chlorine levels frequently during such conditions. Add a sanitizer as needed, according to label instructions.

High pH
Alkaline water prevents chlorine from effectively killing algae. Use a pH decreaser, as directed on the label, to lower the pH to the correct level of 7.2 to 7.6.

Dirty Pool Surfaces
Dirt and slime accumulation on pool surfaces provides the perfect location for algae problems to start. Brush and vacuum weekly to eliminate this source of trouble.

Types and Symptoms of Algae Growth

Types of Algae

Hazy or cloudy water, green water, visible algae growth or an inability to maintain a proper chlorine level are signs that algae could be growing in a pool. Take steps to treat the problem before it makes the pool unusable. There are varieties of algae that can grow in swimming pool water.

Green Algae: The most common type of algae and also the easiest to prevent or eliminate. Green algae are free-floating or surface-clinging and can turn a pool green in a matter of hours.

Black Algae: A filamentous growth on the rough surfaces of the pool. It appears as a thick, black mat or slippery spots on pool surfaces. It also forms a protective coating. Black algae are typically found in plaster or gunite pools.

Mustard Algae: Appears as orange, yellow or mustard spots on pool walls and floors. It often forms on the shaded side of the pool in all pool types. It's easy to brush off but difficult to eliminate. Mustard algae can be resistant to chlorine and some compounds in regular algaecides, so a special algaecide is usually required to eliminate it.

Algae Treatment Preparation

Preparing to Treat Algae with Chemicals

To remove algae from your pool water, you may need to use some chemicals. Before using swimming pool chemicals, read all product labels for directions and safety precautions. If you have additional questions or problems, discuss pool maintenance with a Lowe's associate or call a professional for help. In addition, pool experts recommend that you:

  • Store products in their original containers in a cool, dry and well-ventilated area out of the reach and sight of small children.
  • Never smoke while using pool chemicals.
  • Always add chemicals to the water — never add water to the chemicals.
  • Never add chemicals to the pool while someone is in the water.
  • Never mix chemicals unless the label specifically instructs you to do so.
  • Always wear rubber gloves when handling chemicals.

Solving Algae Problems

Solving Algae Problems

Algae are tiny, microscopic plants that enter a pool by rain, wind or fill water. Green algae are free-floating, mosslike debris in the water. Black and mustard algae can be identified by simply running a hand over a sidewall of the pool. If the wall is slick or oily to the touch, it’s probably from the growth of one of these types of algae. The causes of pool algae growth include:

  • Inadequate, free and available chlorine levels caused by a heavy rain, a lot of swimming or poor maintenance
  • Too high of a pH level, preventing chlorine from killing the algae
  • Insufficient cleaning or brushing of pool surfaces, leaving the surfaces dirty and vulnerable to algae growth

Treat Green Algae

Treat Green Algae

Step 1

Verify that the pool filter is clean and running properly.

Step 2

Test the water to make sure the pH level is between 7.2 and 7.6 and adjust as needed.

Step 3

Add an algaecide following the label directions and allow it to work overnight.

Step 4

The next day, brush and vacuum the pool surfaces. As needed, backwash or clean the filter to remove the collected algae and debris.

Good to Know

Backwashing is the process of reversing the water flow back through the filter to remove debris.

Step 5

For a heavy growth of green algae, perform a second algaecide treatment following the product instructions.

Step 6

As needed, retest the water for pH and total alkalinity. Black algae grows on pool walls and floors as a thick mat that quickly can ruin pool water. Mustard algae appears as yellow or orange spots, typically found on shaded walls and floors. It can be brushed off easily but will likely return if not treated properly. Mustard algae can be resistant to chlorine and some compounds in regular algaecides, so a special algaecide is required to eliminate it.

Treat Black and Mustard Algae

Treat Mustard and Black Algaes

Step 1

Test the water to make sure the pH level is between 7.2 and 7.6 and adjust as needed.

Step 2

Brush and vacuum the pool surfaces using standard pool cleaning tools.

Step 3

Backwash the filter to remove as much debris as possible.

Step 4

Add pool shock following the manufacturer’s instructions.

Step 5

Add a specialized algaecide following the label directions and allow it to work overnight.

Step 6

The next day, brush and vacuum the pool surfaces again. As needed, backwash or clean the filter to remove the collected algae and debris.

Step 7

Repeat the process as needed to thoroughly remove the algae.

Step 8

After the pool water is clear, chemically clean the filter with a filter cleaner.

Step 9

As needed, retest the water for pH and total alkalinity.