What Causes Yellow Algae in Pools | How to Cure and Prevent

Yellow or mustard algae is a shocking word every pool owner or pool cleaning expert wants to avoid. However, once you find it in your pool, it will be challenging to get out of it as it persists for a long time. 

These hard-to-remove ugly algae can ruin the fun of swimming. Furthermore, pool algae will slowly degrade and stain your pool equipment or pool surface. As well as it can become a health hazard. Before it covers your entire pool, learn what causes yellow algae in pools & how you can remove it from your backyard pool. 

From this guide, we will break down the reasons behind growing this type of algae. Also, we will cover what precautions you need to take. So, let’s dive into this article right here. 

What is Yellow Algae?

These algae are microorganisms known as xanthophytes. They can resist chlorine or other sanitizers. You can find this type of algae in southern climates and rarely in northern climes. Often, people can assume it as dirt, sand, or dust mistakenly. 

However, some characteristics let you identify whether it is mustard algae or not. For example, yellow algae or mustard algae hold on to pool walls, pool bottom, ladder, or other objects. 

Therefore, yellow algae are chlorine resistant. It means the algae keeps coming back to your pool though you remove it. The challenging part is- it returns to the same spot. To sum up, it will be very difficult to kill this kind of algae. 

What Causes Yellow or Mustard Algae in Your Swimming Pool?

Yellow algae can grow in your pool for several reasons. Among them, the unusual use of chemicals is the main culprit behind blooming algae in your backyard lake. Besides, unsettled pH or alkalinity levels in your pool may also allow the mustard algae to grow. 

Algae can also spread if algae spores enter your pool with swimsuits or contaminated equipment. A warmer environment is another reason that is responsible for growing mustard algae in your swimming pool. 

Therefore, unbalanced water, poor water circulation, improper pool maintenance, lack of proper filtration, and sunny days are also responsible for spreading yellow algae in your pool. 

How to Test or Diagnose Mustard Algae

Mustard algae look like yellow-green or brown. Unlike other green algae, such algae have dry and powdery surfaces. That’s why most pool owners think of it as dirt or calcium build-up. 

However, you can effortlessly identify whether it is mustard algae or dirt. If you feel it gritty, probably, it will be calcium build-up or dirt. On the other hand, if you feel it slimy, understand it is mustard algae. 

Why Pool Experts Get Terrified When Hear About Yellow Algae or Mustard Algae?

Mustard algae! Why are we getting terrified? Just shock the pool with chlorine and remove the culprit from my swimming pool. 

If you think this way, you are wrong. Mustard Algae are not similar to other green algae. They can resist standard levels of chlorine and also survive in high chlorine levels. In other words, you can’t kill the yellow algae with chlorine shock. 

Another terrifying fact about mustard algae is it returns to your pool quickly in the same area after brushing the algae away. That’s why getting rid of yellow algae is challenging- even pool cleaning experts take a deep breath when hearing the words mustard algae. 

How to Get Rid of Yellow Algae From Your Pool?

cleaning yellow algae

From above, you learned what causes yellow algae to grow and how challenging it is to remove. Yeah, it’s difficult to get the mustard algae out of your pool. But it’s not impossible. From this chapter, you will learn how to get rid of yellow algae with simple steps.

  • Wash your bath suits, pool equipment like a pool filter, hoses, pool toys, pool ladders, floating pool light and pool floats, pads and mats.
  • Use a pool brush to brush away the mustard algae. You can also use a pool vacuum to get rid of yellow algae thoroughly.
  • Test the pool chemistry with help of a pool test kit and balance your pool water according to. Use only standard pool chemicals, never use pond or agricultural herbicides chemicals.
  • Vacuum your pool again with a pool cleaner, pool sucker or suction pool cleaner.
  • Shock your pool with chlorine. Make sure you add 3 pounds of chlorine for 10,000 gallons of pool water.
  • The robotic pool cleaner could do a lot of the jobs. The most amazing feature of an automatic pool cleaner or robotic cleaner is that it will clean your pool surface and walls thoroughly and keep the pool free from debris, preventing the production of harmful algae.
  • Again brush your pool with a pool brush (Nylon brush for vinyl pool surface) and keep balancing your water.
  • In severe cases of this type of algae, you may use algaecide after the brushing step on a weekly basis. Copper algaecide could be an excellent choice for this.
  • Shock your pool again with one lb. of chlorine for 10000 gallons of water.
  • Test your pool water again and make sure there are no algae.

Tips: For future contamination of yellow algae, it is better to use a pool cover.

What Does Dead Mustard Algae Look Like

Mustard algae turn off-white or gray when it gets dead. You must remove the dead algae from your water through filtration. Otherwise, it breaks the ecosystem of your pool and leaves the water toxic. 


So, what causes yellow algae in your swimming pool?

Poor pool maintenance, unbalanced pool water, lack of water circulation, and poor filtration causes yellow algae to grow in your pool. 

We suggest you clean and brush your pool regularly. Also, pool shock once a week with chlorine to close every possible way to grow algae in your backyard pool. 

If the yellow algae come to your pool after taking all of these precautions, follow the above-mentioned methods. Be assured that yellow algae will disappear quite shortly.

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