Swimming Pool Yellow Algae: How to Get Rid Of Mustard Algae In A Pool

Killing swimming pool yellow algae can be a problem. Proper treatment, maintenance, chemical help, and algaecide for your regular and saltwater pool.

You can learn to get rid of and control of these swimming pool problems by using pool tips to have the best pool water quality. Proper pool water maintenance and using the best pool tips are essential in fighting any kind of swimming pool algae.

How to Get Rid Of Mustard Algae 

Mustard deposits are usually found on the walls, primarily on the shady side of the pool.  Unlike brown algae and black algae, this mustard swimming pool algae can be easily brushed away, but it will return without the right kind of swimming pool chlorine and a  good pool shock.

Are you tired of messing with your yellow algae? Has it been weeks since you've used your pool?

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How To Kill Yellow Algae

Balance It Out

Before trying to remove your pool algae problem, bring the pH, alkalinity, and hardness into line.  The pH should be 7.0 - 7.2, alkalinity between 80 - 120 ppm, and hardness is 150 - 250 ppm.  You MUST know what your chemical readings are BEFORE you begin.   

Brush & Scoop It Out

Purchase a high quality leaf rake, (not those simple blue square skimmers) and scoop out as much debris from the bottom and top of the pool as you can. If you're able, make sure the bottom drain is clear and free of debris.  Continuously run your filter.  Watch that the pool’s water level does not get below a minimum of 2” from the bottom of the skimmer.  You want to get rid of the dead algae.  If the water is too cloudy to can skip vacuuming for now. 

Clean It Out

Next is to remove as much out of your as possible which includes pool toys, floats, and ladders.  This includes your leaf rake and brush.  Give everything a good scrubbing with bleach.  Also remember to clean your filter.

Shock It Out

And now it's time for chlorine, and lots of it.  Super-chlorinate, or shock, the pool by maintaining the FC level to 15 - 20 ppm.  If your pool chlorine is 1.0 ppm then raise it to 15 ppm or  slightly above. You must do this in order to kill the algae. Don’t skimp on the pool shock.  I suggest using liquid pool chlorine instead of granular chlorine, a.k.a. Calcium Hypochlorite, to shock your pool.  Brush, and I mean really brush, the bottom, sides, and steps to loosen any yellow algae that may be adhering to the surface.  You will want to maintain a high FC level of 15 - 20 ppm for at least 24 hours after the water clears.

Test Your Pool Water

Get Rid Of Yellow Algae

You must reach that 15 ppm or above because if you don’t it’s just wasting time and money.  Coming close won’t cut it.  Get a good water testing kit and learn how to use it.  Test strips will NEVER give you the chemical numbers your need.  Remember the color "RED" on a test strip is not a substitute for a FC chemical number. 

To super-chlorinate you must do this all at once, not over a few hours or days.  If you're running your pool chlorine at 1.0 ppm, then bring it up to 15 - 20 ppm.  You’ll notice this is working when your yellow to a white or grayish. Also, there might be be dead algae on the bottom of the pool. This can be filtered out through vacuuming the bottom of the pool. Keep brushing and vacuuming to rid the pool and any residual yellow algae and remember to keep filtering and back-washing to get rid of the swimming pool algae.

If you have a DE filter, you'll need to re-coat or recharge the grids with each backwash.  If you have a cartridge filter remember to take the filter out and clean it once per day with a regular garden hose, never a power washer.  Brush and filter then brush and filter and then after you do those it’s time to brush and filter some more.  Once this step is finished you'll want to maintain a high FC level for at least 24 hours. 

Remember, when you have a swimming pool algae problem, there is no quick fix. It will take time, effort, and patience to clear up your pool.

Word Of Caution

If anyone says to you, "Oh, you have mustard or yellow algae in your pool?  Let me tell you how to clear it up.  First, get the pH and alkalinity in line.  Then shock the pool and add a clarifier.  If that doesn't work, put 2 tabs in the skimmer and add a couple bottles of phosphate remover and circulate the water for 24 hours.  If that doesn't work, add some algaecide and put another tab in the skimmer."  Does that sound familiar?  It just might.

Folks, I've been doing this pool gig since 1999.  I've cleared up over 700 pools in 3 different states (Arizona, Oregon, and Florida).  All had different locations, different cities, different temperatures and climates with different water sources.  I absolutely guarantee that advice will cost you hundreds of dollars, countless hours, and your Summer will be ruined.  It's virtually impossible to clear it up a pool without the right information and the proper understanding of pool chemistry that applies equally to every chlorine and salt pool in the world. 

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Get Rid Of Yellow Algae


When your swimming pool chlorine is down to 2 - 4 ppm the pool will be safe to swim in once again.  At this point you can use a clarifier to help with the filtration.  Obviously you would NEVER allow anyone to swim in the pool until the swimming pool algae and/or mustard deposits are gone and the water has cleared up.  Treating algae can be a little tricky.  It's one of those kinds of algae that seem very harmless because it can easily be brushed away.

I like calling mustard or yellow algae "ghost algae" because it disappears easily by brushing, but then it comes back the next morning and you say, "Where did that come from?" Don't let this fool you, because it will come back again and again unless you take the right steps to rid your pool of this pain once and for all. 

Happy Swimming 

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What Others Have Said

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Recurring Mustard Algae And Fed Up! 
We are renting a house with an 10,000 gallon in ground saltwater pool with a cartridge filter. For the third time in a little over a year we have mustard …

Rust In The Pool That Looks Like Algae 
Pool water is clear but the walls, steps, and floor looks like rust. I think it is algae. It will not rub off. I put in Yellow Out, shock, algaecide 60, …

Fine Powdery Yellow/Light Brown Substance..Algae Problems 
I have trouble keeping my in-ground pool clean. There is a very fine powdery yellow / light brown substance I can't vacuum out. Chlorine / pH levels are …

Dead mustard algae Not rated yet
My problem is that I can't get the dead gray looking algae out of the pool. I have a DE filter. I vacuum and backwash (many times now) and it keeps returning, …

Mustard algae that won't die Not rated yet
We have been fighting this since we opened the pool. Didn't realize it was mustard algae for sure until within the last month. We were with a pool store …

Correct Test Readings With High FC Levels Not rated yet
I use the TF-100 test kit. Readings are FC-16, PH-7..5, TA-100, CH-220 and CYA-40. 16,000 gal. White plaster pool in full sun. Problem is I'm using …

Cannot Remove My Brown/Mustard Algae Not rated yet
I have a DE filter. All my levels are good. I came from the pool store wondering why I have algae with a good chlorine level? They wanted to give me …

White Powdery Sediment On Bottom/Sides Of Pool Not rated yet
After having my water analyzed I added soda ash, then alkalinity up and finally Phosfree. I ran the pump for 48 hours and the water turned cloudy. …