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Mustard Algae in your pool: what you should know about it

How to get rid of Mustard Algae

There are certain colors in your swimming pool that we would imagine you hope to never see. The yellowish hue of what is sometimes called mustard algae is a really good example of what we are talking about. This isn’t some alien invader, although it’s going to look particularly strange in your swimming pool. This is another form of algae that can cause a variety of issues. However, this is made worse by the fact that yellow algae are quite rare. Because of this, it can prove to be one of the most relentless, damaging intruders to come to your pool.

If you ignore the problem in the present, this yellowish mold can become an absolute nightmare later on. Dealing with a serious yellow algae situation can be costly and time-consuming. To be sure, it can bring your swimming pool season to an abrupt, unfortunate end.

Thankfully, it doesn’t have to be this way. Taking care of yellow algae is in fact a simple enough matter. This is dependent upon not only understanding what you are dealing with, but keeping in mind what you will want to do to eliminate this pest forever. There are also preventative measures that can naturally be taken if you don’t want to deal with mustard algae ever again.

We’re going to cover everything in greater detail. Let’s start with a deeper look at exactly what we’re talking about.

What Is Mustard Algae?

Yellow algae can be seen as a cousin of the considerably more well-known green algae. While green algae is annoying enough on its own, yellow algae presents a certain element of persistence that can drive swimming pool owners absolutely nuts. With green algae, you probably already have a rough idea of what we are talking about. You know about its sliminess, as well as the fact that it likes to stick to the walls of your pool or create disgusting greenish blobs that float around in the water. Such fungus can usually be traced to a failure to take care of the pool correctly, but there are other things you can potentially blame green algae on.

Yellow algae can come to us from a similar background of negligence. It is particularly popular in warmer, southern climates, but it is not impossible for it to make an appearance in a colder climate. What makes it arguably worse than its green cousin? You can start with the fact that its more similar in appearance and even touch to sand or dirt. It can look like a stain in or on your swimming pool, as well. This member of the xanthophytes family is highly resistant to chlorine, which is why it can potentially appear even under ideal circumstances. It is also considerably harder to destroy than green algae.

Why Is Yellow Algae So Hard To Kill?

Like green algae, the yellow variety likes to cling to the walls and similar surfaces/areas of your swimming pool. However, yellow algae will take things a step further, as it seems to love attaching itself to just about ANYTHING it comes into contact with. Your swimming pool equipment and accessories, pool toys, and floats are all susceptible to becoming “infected” with mustard algae.

Yes, even your swimming trunks can pick up this disgusting stuff.

To be clear, yellow algae is not going to seriously harm you. At the same time, it stands to reason that you would like to eliminate this disgusting yellowish mess from your swimming pool once and for all. This will require a few aggressive steps, but it can absolutely be done. More to the point, there are also steps that can be taken that will ensure a strong likelihood of never having to deal with mustard algae ever again.

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How Do I Kill Yellow Algae In My Swimming Pool?

At this point, you can see the severity of the problem in front of you. Yellow algae is unlike just about anything else that can wreak havoc with the comfort and even the safety of your swimming pool. There are all kinds of things you can do. However, we are going to take the most aggressive stance possible, when it comes to getting rid of this stuff.

To that end, here is everything you are going to want to do, if you want to be absolutely certain the yellow algae has been destroyed:

  • Clean your toys and accessories: With a clean cloth, as well as a good chlorine-based cleaning product, start to comprehensively wipe down everything you own that has come in contact with your pool recently. We mean everything, and we certainly mean comprehensively. Avoid using actual bleach, as this can damage the plastic and similar materials used to make these products.
  • Wash your swimming trunks, towels, etc: This is where a regular bleach will do just fine. Our suggestion would be to run everything through a normal cycle on the washing machine. If you don’t want to use a regular-type bleach, try a color-safe one instead. You will want to use at least something that’s stronger than your normal detergent.
  • Move your equipment: nets, poles, and similar pool care items have probably come in contact with the algae. Thankfully, cleaning this stuff is not difficult by any means. Move it over to the shallow end of your swimming pool, or simply leave it in the water. It can be left there for a step we’re going to discuss shortly.
  • Brushing and vacuuming: This is where things can get a little intensive. You are going to need to work hard at brushing and then vacuuming every single trace of the mustard algae. The brush is going to be essential for loosening up algae for removal by the vacuum. You will want to manually vacuum, as opposed to using a robotic version. Make sure your filter is set to waste and be certain to replace any freshwater you used up while vacuuming.
  • Testing to create a balance: Testing and balancing is your next step. We’re going to be shocking your pool pretty soon, so testing (in order) your alkalinity and pH can help you figure out the ideal levels for what you’re going to do next. Your ideal alkalinity should be approximately 100-150PPM (Parts Per Million). Your ideal pH will be around 7.4 to 7.6.
  • Another brushing: Yes, you read that correctly. You want to get rid of everything you may have missed the first time, with the remnants floating in the water. We’re almost at the shock point of this whole process. Everything we are essentially doing now is designed to make that aspect of things as effective as possible.
  • The shocking: Yellow algae is a big problem, so it demands a big answer on the shocking front. This is the process of blasting/shocking your pool with ideal chemicals. We would suggest a triple shock, which means using three pounds of shock per ten thousand gallons of water. The best window in which to do this is in the early evening. You will then leave your filter and pump running, as long as it takes until the algae is eliminated.
  • More brushing: Go for another round of brushing, combined with another round of making sure your levels are optimal in every possible way.
  • One more shock: Give yourself 2-3 days at this point, before applying a final regular (one pound or so per ten thousand gallons) shock to your pool. This should indeed utterly and completely eradicate the presence of yellow algae.

Make sure you keep your swimming pool equipment, the stuff you left in the water, soaking throughout all of this. After you have completed the final round of shocking, your next step will be to test the waters of the pool one more time. If the balance of your water’s chemistry is nominal, then you have taken care of your troublesome mustard algae problem! Congratulations!

However, in order to ensure this stuff never troubles you again, there are a few very basic preventative measures you can remember.

How To Make Sure Mustard Algae Doesn’t Come Back

Let’s wrap up by covering a small checklist of preventative measures. Trust us when we tell you that you really don’t want to deal with getting rid of mustard algae more than once in your life!

  • Keep your water levels balanced at all times. This is basically the frontline of your defense against all contaminants in your swimming pool, including yellow algae.
  • Keep up a regular schedule of maintenance. This includes running the pump and filter as instructed by your owner’s manual. Regular brushing and vacuuming are smart, too. For maintenance purposes, a robotic vacuum will work just fine.
  • Keep shocking the water: Around once a week, again, in the early evening, add a regular shock to your swimming pool.
  • Keep cleaning after use: From your pool floats, to your pool toys, and to anything else you may use, strongly consider a gentle spray with water, followed by a quick wipe-down with your chlorine-based cleaner. Nothing as strenuous as what we suggested above.


If you really want to avoid calling the professionals, keep in mind everything mentioned here. You should be just fine.

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