Why is the Water Green? How to Kill Pool Algae

The green color of your pool water is the result of algae growth. There are several reasons algae may begin to bloom in your swimming pool, including:

• Not enough chlorine

• pH not balanced

• Poor water circulation or filtration

• Increased water temperature

• Lots of swimming

Even when you notice the beginning of algae growth, you might be tempted to go for a swim. After all, the water isn’t that green. Plus, ponds and lakes are filled with algae and you swim in those, right?

However, no matter how slight your pool algae problem, it isn’t a good idea to swim in green pool water. Many kinds of bacteria feed on algae, and bacteria can cause multiple health problems. According to the Centers for Disease Control (CDC), the most common swimming-related illnesses are diarrhea, skin rashes, swimmer’s ear, pneumonia or flu-like illness, as well as eye and respiratory irritation.

It’s better to be safe than to risk introducing swimmers to potential health issues.

Algae isn’t good for your swimming pool, either. In addition to making your pool surfaces slimy and slippery, algae can clog your pool filter and limit water circulation, making your algae problem even worse. Algae can also permanently stain your pool.

Algae is a living organism. Like a plant, it survives through photosynthesis, a process that relies on sunlight, water and carbon dioxide. However, algae lacks the leaves, roots and stem of a true plant.

Just as there are many different types of plants in our gardens, there are several types of algae that can invade your pool. Pool experts identify algae varieties by their color.

Green - Green algae is the most common swimming pool algae. It can appear blue-green, yellow-green or dark green. Even before you see it, you might notice it as a slimy film on pool surfaces. Green algae can turn a pool green overnight. The sooner you treat it, the easier it will be to get rid of it.

Yellow - Also known as “mustard algae,” yellow algae is easy to overlook or mistake for sand, dirt, stains or pollen deposits. You’re more likely to find it in the shadier parts of your pool. Yellow algae is very resistant to chlorine, so you’ll need to attack it with a heavy-duty shock treatment.

Black - Although technically a dark blue-green algae, black algae appears like slimy black spots in pool cracks and crevices. It thrives in shady areas of the pool. While rare, black pool algae is extremely difficult to eliminate. You may need to use a product made specifically for black algae.

Pink - Pink algae is actually bacteria, not algae. You’ll usually find it growing on plastic pool parts like the skimmer, ladder, return jets and pool floats. It doesn’t “bloom” like green algae and is easily prevented by maintaining optimal chlorine levels.

Whatever type of algae is growing in your swimming pool, the steps to treat it are similar.

Getting rid of swimming pool algae requires several steps.

Test your pool water: Use a pool water testing kit to measure the pH, alkalinity and chlorine levels in your pool. Water chemistry that is out of balance can contribute to algae growth.

Brush and vacuum: Brush the sides and bottom of the pool to loosen any algae that has formed. Then, vacuum the pool to remove the algae and other debris. Set your vacuum to “waste” so the algae doesn’t recirculate in your pool.

Add flocculent if necessary: Adding a flocculent may help when treating a large algae problem. Pool “floc” causes algae to form clumps that are easier to vacuum up.

Shock the pool: To kill algae in the pool, "shock" the pool with a high dose of chlorine or other sanitizer. This will kill any remaining algae spores. Follow the manufacturer's instructions to calculate the proper amount of shock treatment to use, based on the size of your pool. Shock is best accomplished in the evening or at night. This keeps the sun from leaching the chlorine from your pool before it can go to work.

Run the filter: Swim University recommends running the filter for at least eight hours or overnight to make sure the shock treatment is thoroughly mixed into the water. Your pool water may turn cloudy, but continual filtering should clear it up.

Unfortunately, you won’t kill pool algae overnight, notes Trouble Free Pool. Algae is constantly growing and you have to stay on top of a problem when it occurs. Realistically, it might take 48 hours or longer for your pool to be algae-free. Be patient while correcting the situation, then take steps to keep algae from forming in the future.

Maintain proper pool chemistry: Once the algae is gone, maintain proper pool chemistry to discourage new algae growth. This includes regularly testing and adjusting the pH, alkalinity and chlorine levels, as well as ensuring proper circulation and filtration. Out of the entire pool chemistry system, chlorine is the single most important additive to keep algae from forming.

Use an algaecide regularly: If you often have green algae in your pool, you may want to use an algaecide to prevent future growth. Be sure to follow the manufacturer's instructions carefully. Avoid overuse, as this can cause other water chemistry issues.

Pool algae typically creates higher pH levels in the water. This encourages more algae growth, causing pool pH to become even more unbalanced. Maintaining optimal pool pH (between 7.4 and 7.6) is one way to keep algae from limiting your swim time.

Algae is introduced to pool water from outside sources, including clothing, pool toys and the wind. Suggest that swimmers bathe or at least rinse off before entering the pool.

Algae also can hitch a ride on floats and clothing that were used in a natural body of water. So wash bathing suits and pool toys regularly, especially after a day on the river or at the beach!

When your pool is not in use, a pool cover helps keep algae spores and spore-carrying debris from being blown in by the wind.

To prevent algae from forming, brush and vacuum your pool regularly. Pay special attention to problem areas like pool corners, under ladder steps and inside skimmer boxes.

Make sure the filter is clean and that the filtration system is working well. Without proper filtration, algae can grow even if chlorine levels are high, notes Garden Gate.

Sanitize your pool regularly, keeping chlorine levels within the recommended range.

It’s important to address algae growth in your pool as soon as possible. You’ll protect your family’s health and safety and help prevent costly pool maintenance and equipment repairs. And you’ll enjoy fewer lost swim days!

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