How to treat algae in a swimming pool

How to treat algae in a swimming pool

Today I’m going to show you how you can get rid of mustard algae in your pool FAST.

By following the steps in this guide, you will get rid of the dreaded mustard algae once and for all .

And hopefully never see it return ever again.

You’ll also learn what you should be doing after treating your swimming pool for mustard algae to make sure you’ve actually killed it.

What is mustard algae & why is it bad for your pool?

Mustard algae (also know as yellow algae) is actually another form of green algae, but it varies slightly in color: it can be yellowish, yellow-green or yellow-brown.

The problem with this pesky little nuisance is that it looks so much like dirt, pollen or sand, that often, people don’t even realize they have it.

It’s also not slimy like other algae, so it even has a texture close to that of dirt. But, why is it bad?

Well, algae itself is not dangerous to humans, but an overgrowth of it can harbor harmful bacteria that is dangerous, such as E coli.

Also, like any other algae, it can stain your swimming pool and cloud the water, which also sticking to things like pool equipment, pool walls, bathing suits, floats and toys. Nobody wants to swim in that mess!

This type of algae usually requires chlorine plus an extra chemical like Yellow Out to finally get rid of it.

Mustard algae is most commonly found in freshwater or warm water climates, but that doesn’t mean you shouldn’t keep a look-out for it anywhere you live.

How to prevent mustard algae from growing in your pool

Although mustard algae is more closely kin to green algae, it is just as hard to get rid of as black algae.

I know. I tried to keep from saying the “b” word. But it’s true, and if you let mustard algae get out of control, you might find yourself having to drain and acid wash your pool.

And nobody wants that!

The best way to get rid of algae is to never get it in the first place!

How do you do that? I’m glad you asked!

There are several things you need to be doing on a regular basis to keep mustard algae at bay.

Algae is a major concern for any pool owner, but it is also easily preventable with the Sustain 3-Part System. Sustain is a high-quality product line that’s been proven effective at producing clean, sparkling, algae-free water for more than 25 years. In fact, it is so effective that the Sustain 3-part System comes with an Algae-Free Limited Warranty.

There are four general classes or types of algae found in swimming pools. The chart and information below will help you to identify and eliminate each:

Check filter for proper operation and clean if dirty.

Use Sustain Shock Treatment according to label directions.

Maintain 1-3 ppm Free Available Chlorine (FAC). Re-dose Shield if

Yellow (Mustard) Algae

Yellow algae is sometimes called mustard algae and appears on the pool surfaces as a fine dust. Typically, it is seen first on surfaces that don’t receive direct sunlight. This algae is easy to brush off, but it frequently returns. Most pool experts agree that this type is the most difficult algae to control. Use Sustain Shock Treatment according to label directions and thoroughly brush the pool surfaces. Cleaning the filter and other equipment is especially important in controlling Yellow Algae. Circulate continuously and backwash the filter, cleaning the element as needed to maintain good circulation. When the problem is under control, backwash the filter and clean the element regardless of the back-pressure/flow rate. This will rid the pool and equipment of any algae that may remain trapped in the filter.

Black Algae

Black algae grows on the pool surfaces as dark spots. These colonies of algae will usually form in areas with less circulation. Black algae will feel slimy and will brush off with some effort. The algae grows into the pool surface and will be difficult to completely remove. Use Sustain Shock Treatment according to label directions and brush the affected areas frequently. Circulate continuously and back-wash the filter, cleaning the element as needed to maintain good circulation. When the problem is under control, backwash the filter and clean the element regardless of the back-pressure/flow rate. This will rid the pool and equipment of any algae that may remain trapped in the filter.

Pink Algae

Pink algae is actually bacteria. It forms colonies that have a slime layer. Pink algae is common in pools located near the oceans and Gulf waters, but can also show up inland, especially when swimmers have recently returned from vacationing on the coast. Use Sustain Shock Treatment according to label directions and brush all affected areas thoroughly and frequently. Wash all swimsuits and toys with dilute bleach. Circulate continuously and back-wash the filter, cleaning the element as needed to maintain good circulation. When the problem is under control, back-wash the filter and clean the element regardless of the back-pressure/flow rate. This will rid the pool and equipment of any colonies that may remain trapped in the filter.

by CityWide | Apr 12, 2021

How to treat algae in a swimming pool

It is officially springtime in regards to our temperatures in Las Vegas and green pools become more and more common every day. You can find them in vacant homes, residential swimming pools, commercial pools, or in any pool that isn’t properly maintained. This also occurs in the springtime because homeowners forget to increase their chlorine levels and filtration run times. We think it is extremely important to tackle this issue in a variety of different ways so we hope this blog post gives you a better understanding of why this happens and all the different factors that go into turning that green pool blue again because now more than every keeping pools sanitary is extremely important! Typically, you will see a direct correlation to green algae-filled pools with a lack of chlorine or poor filtration. Whenever you have warm water, algae loves to grow and if you don’t have the proper amount of chlorine in the water, algae will grow rapidly! The same goes for filtration, if you’re not filtering your swimming pool long enough your chances for algae growth increase. The following are the most common issues for algae to grow:

  • High phosphates
  • High Cyanuric Acid (CYA/stabilizer) levels
  • Lack of chlorine
  • Minimal filtration times

Balancing Water Chemistry

When it comes to water chemistry, checking your phosphates regularly is important. Phosphates come from vegetation, soils, and fertilizers which are food for algae. When phosphate levels increase in the swimming pool they must be removed because no matter how much chlorine you use, algae will still grow. Typically, with high phosphates, you will need to purchase a phosphate remover and phosphate test kit if all your other chemistry levels are within normal ranges. Other factors could be high CYA levels. CYA helps reduce chlorine loss by protecting the free chlorine in the pool from the sun’s ultraviolet rays, reducing the amount of chlorine needed to maintain proper sanitizer levels. When these levels get too high, it lessens the effectiveness of chlorine to act as a disinfectant. Higher levels will bind with the chlorine, making it slower acting to kill bacteria and micro-organisms, and prevent algae from growing! This typically occurs because chlorine tabs have stabilizers in them. As a side note, the factor needed for Free Chlorine (FC) in relation to CYA is 0.75. This means if your CYA is 150 ppm you will need 11.25 ppm FC to combat algae. That is why optimal levels of CYA in your swimming pool should be between 30 – 50 ppm.

How To Treat Algae

When you’ve determined where the growth is coming from, City Wide Pool Service recommends the following steps to help remove the algae:

  • Identify the type of algae
  • Check chlorine, pH, and phosphate levels
  • Check all pool equipment for leaks
  • Check filtration equipment for tears in the filter grids or old sand
  • Check run times for filtration (at this point you should be a minimum of 8 hours daily)
  • Balance your water chemistry

If any of the above is the issue, the addition of more chlorine or increasing your filter run times should help because it is the two most common reasons why it occurs. Remember, clean it regularly and balance your water chemistry. If you do both of those, you should be able to keep your pool looking great. If you should have any questions, please contact us today!

Are you wondering what the best way to treat green algae in your swimming pool?

So, you pull that winter safety cover off the pool after a long hibernation or walk into your backyard after vacation and instead of uncovering a refreshing watering hole you discover it’s more of a swamp. Fear not! This is a common issue and there is a solution. The first thing to do is NOT to run to the local pool store. Don’t forget YOU are a chemical expert and you can do some recon work on your own!

“This is not a fast process, so if it takes you 7-10 days to complete the process don’t be shocked. For really bad cases it can take up to 2 weeks.”

Here is the best way to treat green algae:

Step 1

If you can see the pool floor vacuum to waste, then grab your test kit. If you can’t see the floor just go straight to the kit for now. Resist the urge to just start throwing shock and algaecide in willy-nilly. Balance your alkalinity and pH first. Remember that alkalinity stabilizes pH and chlorine is more effective with a pH neutral pool. Balance these two items and give your pool a minimum 6 hours to circulate and 12 if you are extra patient. Then test the chemicals again and if the alkalinity and pH still isn’t right complete another treatment.

Step 2

After 2 treatments test your chemicals again. Make sure the Alkalinity and pH are still maintaining the proper balance. If they are then today is the day we add shock. In order to kill green algae, you must raise the chlorine level to 30 ppm. In the back of the Taylor test kit book there is a chart based on how many gallons of pool water you are treating. It will tell you exactly how much to add. Do not add the shock directly to the pool. The granules can sit on the pool floor and cause damage to the surface. Get a 5-gallon bucket, fill it up with water from your pool water and add the shock to the bucket. Stir it up with an old broom handle or the like. Walk around the pool dumping the mixture in. If there is still granular shock in the bottom of the bucket, add more water and repeat the process until all the shock is in the pool. Once that is done brush the entire pool. You should notice that the green color is starting to change and you may even see patches of milky white or lighter green color. The algae does this when it is dying. By brushing the pool, you are weakening the algae and exposing it to the chlorine you just added to the water.

Step 3

If your pool is mostly a milky cloudy color and you cannot see the bottom this is good. It means we are making progress. Test your chemicals again. If the chlorine is above 10, wait to add clarifier. If your chlorine is too high it will actually break down the clarifier so it can’t do its job, so you are wasting chemicals and money. If you are in a hurry I would recommend a product called Revive! This product is a flocculant (drops particles to the bottom) and a clarifier (brings the dead algae together so it can be filtered out more easily). It does a few other things too that you can check out on the link above. The best part is that Revive will not break down with high sanitizer levels. You can add it if the chlorine is as high as 30 and it works fast. If you don’t want to use Revive hang tight and give your pool another day for the chlorine level to drop before adding clarifier.

If your pool is still green dose it again with shock and make sure you are maintaining that 30 ppm level and brush the pool again. You should also complete a backwash on day three so you get some of the dead algae out of the pool filter.

Step 4

Complete a vacuum to waste. If you don’t know how check out the step by step instructions on how to vacuum to waste right here on this site. By vacuuming to waste you are bypassing the filter and all of the water is exiting your through your backwash line which will drain your pool a bit but it also doesn’t kick the dead algae you are vacuuming back out to your pool.

Step 5

Repeat the steps for day 4. Continue to vacuum to waste and backwash your filter. Once your pool is clear, now is the time to add your 90 day algae remover. Algae prevention and remover isn’t ideal for removing green algae as it requires the high chlorine level to actually kill it. Algae prevention and remover helps prevent outbreaks, but once you have an outbreak you need to use chlorine. Using only algae remover will get costly and you will end up having to hyper chlorinate your water anyway.

This is not a fast process, so if it takes you 7-10 days to complete the process don’t be shocked. For really bad cases it can take up to 2 weeks. You may need to allow 24-36 hours for each step to work. I would give a day between step 2 and 3 and a day between step 4 and 5 for the chemicals and your filter to work. Normally I don’t encourage daily backwashing, however, it would not be a bad practice during this treatment plan. If you have any questions on where to get the chemicals or if you want the pool pros to help you out with this process click here.

Now you have been through the process make sure you are regularly testing chemicals so you can spend more time enjoying your pool and less time working on it! Prevention is better than reaction and testing chemicals is your best prevention and your best defense against our nemesis the algae bloom.

Not all pool algae is created equal. Identifying your type of pool algae is the first step to curing your algae woes for good.

Not all pool algae is created equal. There are three main types of algae that are found in swimming pools: green, mustard and black. Green pool algae is the most common type and the easiest to treat and prevent. Green algae usually floats freely and may result in green-looking pool water.

Mustard pool algae clings to your pool surfaces and may resemble yellow or brown dust or slime. This tough to treat algae can reoccur and is resistant to chlorine. Black pool algae are the most stubborn. Black algae attach firmly to pool surfaces and form a protective crust.

Identifying your type of pool algae is the first step to curing your algae woes for good. Follow these steps to treat and prevent all types of pool algae.

Test and Balance Water

Always begin by testing your pool water. Your test results will tell you if your water parameters are unbalanced. Pay special attention to your Free Chlorine level. Low Free Chlorine can cause algae to grow in your pool water. Always maintain Free Chlorine between 1 -4 ppm. If needed, apply the appropriate chlorine and sanitizers to restore adequate sanitizer levels.

Clean Pool Water and Surfaces

Skim water surface to remove visible debris, brush walls, vacuum and empty skimmer baskets to clean pool surfaces. Concentrate on areas with visible algae and little or no circulation. Cleaning your pool regularly is an effective step to prevent algae growth.

Apply a Shock Treatment

Crystal clear water starts by applying a pool shock. Shocking your pool water helps to remove contaminants that may cause algae to grow and helps to improve water filtration.

Apply an Algaecide

Select an algaecide specially formulated to treat your type of pool algae. After treatment, some dead algae may remain in your pool. Continue to thoroughly brush your pool’s surfaces often.

Clean Filter

Backwash or chemically clean your filter, according to your owner’s manual, to remove dead algae, organic contaminants and mineral build up. Allow your pump and filter to run continuously for 24 hours so that your pool’s entire gallonage has the chance to run through your clean filter.

For best results, test and balance your pool water weekly. Download the Clorox® Pool app for expert water analysis and product and dosage recommendations. If your algae persists, contact us to help further troubleshoot.

How to treat algae in a swimming poolDuring the months of July and August, algae can be a very big problem for swimming pool owners. With the higher temperatures during these months, as well as inconsistency in a pool’s sanitizer levels, algae can rear its ugly head.

Algae is a single-celled plant form. It uses the process of photosynthesis to manufacture its own food. It comes in a very wide variety of colors and forms, making it adaptable to almost any condition.

Due to algae’s microscopic size, it takes literally millions of these plants to accumulate to be noticed by the naked eye! By that time it may be too late and very costly to correct.

As we tell all our customers: The best way to eliminate algae is through prevention! (This is also why we are such proponents of salt water chlorine systems.)

This article will discuss the different types of algae and how to deal with each.

What are the types of algae, and how do you remove them?

  • Green algae can cling to the wall or float in the water. Get rid of it by brushing the pool, shocking, and adding Algaecide 60.
  • Black algae looks like black spots and feels slimy. Get rid of it by aggressively brushing the algae and adding Algaecide 60.
  • Mustard algae looks like sand in the bottom of the pool. Get rid of it by aggressively brushing the algae and adding Algaecide 60.
  • If the pool is full of algae, add a flocculant (floc) to the water and vacuum up the coagulated algae that settles on the bottom of the pool.

Green Algae

The most common form of algae in swimming pools is “green” algae.

Green algae varies in color from blue-green to yellow-green to dark-green. It can be free floating in the water (turning the water a hazy green) or can cling to the wall-clinging (patches of green).

Green algae can be treated fairly simply with the right amount of brushing, shocking, and algaecide.


Properly analyze the pool water to ensure the pH is at the proper level. Balance the water chemistry if needed.

Pools treated with chlorine should be brushed thoroughly, then shocked, raising the chlorine levels above 3 ppm.

Also, add a strong dose of Algaecide 60 to the water. Continue to check the pool’s filtration throughout this process to ensure proper water flow.

You may have to repeat this process a few times in order to eradicate the algae 100 percent.

Black Algae

“Black Algae” is actually blue-green algae. It forms in cracks and crevices on pool surfaces, especially plaster finishes.

We normally find black algae growing in, but not limited to, shady areas of the pool. Black algae is more typically found in concrete or plaster finished pools because of their rough surfaces.

It is known for a heavy slime layer and “skeletal growths” that make it impervious to normal chlorine levels.

Black algae usually doesn’t change the water clarity. It just makes your pool appear to have black spots on the surface.


Properly analyze and balance the water.

Prior to and during treatment, you MUST thoroughly brush the algae in order to “break open” the slime layer. This is a critical step. If you skip it, you’ll prevent the treatment from working.

Shock the pool very aggressively and continue to brush the black algae. Add substantial amounts of Algaecide 60.

Mustard Algae

Mustard algae is a chlorine-resistant form of green algae (yellow-green to brown in color).

It often resembles dirt or sand on the bottom or sides of a pool.


Same as black algae.

In certain cases, when a pool is full of algae, you have to vacuum the algae directly out of the pool.

You can do this by brushing the algae off the walls, then adding a ‘floc’ to the water. It coagulates the algae and causes it to settle. Once it settles, vacuum it directly out of the pool.

When attempting to floc a pool, follow the directions on the bottle very carefully.

Hopefully you will not be burdened with algae in your swimming pool this year.

As I mentioned earlier in the article, salt chlorine generators are the best way to prevent algae in your pool. They produce a consistent feed of natural chlorine into your pool all the time. They will also allow you as a pool owner to leave for a few days without being too vigilant of your pool, but still come back to a crystal-clear, algae-free body of water.

I’m always amazed at how many pool owners think that algae a standard part of swimming pool ownership. This clearly does not have to be the case, as we have many customers at River Pools who have never even seen algae in their swimming pool. Of course, this is also why just about every one of our customers uses a salt chlorinator.

Good luck and happy swimming!

How to treat algae in a swimming pool

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Editor’s note: This blog article was originally published in August 2009 and has been updated and revamped for accuracy and appearance.

What is black algae?

Black algae is a super resistant and hard-to-kill algae strain. It appears as small, black dots or blotches on your pool’s walls, floors and surfaces. These spots are pin-head to quarter sized. Black algae has a hard outer shell that protects the cells inside. Pools with porous surfaces like concrete, gunite and exposed aggregate are more susceptible to black algae because it can penetrate and grab hold of the walls. Removal can be difficult, but not impossible with the right tools.

How to treat algae in a swimming pool

How do I Get Rid of Black Algae?

There are 2 products you will need. The first is Suncoast Metal Control. This product, which contains calcium, softens the outer shell. This makes it easier for the algaecide to work. The other is Suncoast Super Black Algaecide. This fast-acting, concentrated algaecide is specifically formulated to kill black algae. Finally, you’ll also need a pool brush with stainless steel bristles to clean the walls and other surfaces. Here is what you need to do:

Step 1: Adjust the pool water pH to the normal range of 7.4-7.6 and the alkalinity to within 80-120 ppm.

Step 2: Brush all the black spots with a wire algae brush (use a nylon brush for vinyl, fiberglass or painted pools).

Step 3: Add 1.5 quarts of Suncoast Metal Control per 10,000 gallons.

Step 4: Mix Suncoast Super Black Algaecide into a bucket of water and pour away from the sides of the pool. Use 12 oz. per 10,000 gallons.

Step 5: Brush the black spots daily while algae is visible. *

*For severe cases, consult with the experts at your local Pinch A Penny . You may need to repeat this process or increase the dosage requirements.

How do I Keep Black Algae From Coming Back?

Black algae is more likely to come back after an initial outbreak. Use Suncoast All in One Algaecide to prevent future algae breakouts. This is the best multi-purpose algaecide. It keeps your pool algae-free without foaming and contains a clarifier to keep your water sparkling. It is recommended that you use All in One on a weekly basis as part of your pool maintenance routine. Keeping your pool properly treated and balanced is the best way to prevent algae blooms from returning.

Warning: Please read all bottles and observe all warnings and printed precautions. Use safety equipment. Never add water to chemicals when mixing, add chemicals to water.

Black algae is a problem for many swimming pool owners.

When you wake up and find black algae spots on your pool surfaces, disaster has descended on your pool.

Black algae spots occur in a swimming pool when your water has low free chlorine level and/or dirt is allowed to build up on the surface preventing the chlorine in the water from reaching the surface for a period of time. Good circulation is a must!

Weekly brushing moves the water right near the surface and gets most of the dirt off. It’s a must. No matter the cleaning system, there are low flow spots. Brushing gets the chemicals moving with the water flow created by the brushing.

The time took to avoid black algae is well worth your time and energy.

It is best to handle this problem quickly! As soon as you see black algae spots. Do not wait until you have a major job to handle.

What can I do?

The best and maybe only cure for black algae is a new pool surface. If you don’t want a new surface at this time, here’s a way to get some control on an out of control problem.

Get ready to roll up your sleeves and do some work. Black algae spots are resistant to chlorine! They have a protein layer that keeps them safe from chlorine in the water. Just shocking/chlorinating or dispensing an algaecide in your pool will not rid you of black algae. You have to treat the surface where the Algae lives and not just the water.

There is no easy way to get rid of black algae. It will take Direct treatment with a stabilized form of chlorine muscle power and the correct additional chemicals to get this this problem under control.

I wish I could tell you this was going to be a permanent fix but even if you knock the heads down one week, they can come right back the next.

The Phoenix Pool Expert has a plan! Here’s how you deal with it.

How to treat algae in a swimming pool

The supplies you will need to handle black algae spots are a wire pool brush, stabilized chlorine in tabs for the walls and granular for the floor. Shock won’t do, liquid would be wasted, Granular trichlor is the way to go.

If you want the most bang for your buck, add copper or silver algaecide. The reason we use copper and in extreme cases silver is because they will penetrate the surface and stay there. Other types of algecide are for the water only.

These directions are not for a vinyl lined or fiberglass pools. Contact the Phoenix Pool Expert if your vinyl or fiberglass pool develops a resistant algae.

Do not swim in your pool during the black algae spot treatment.

Here are the steps:

  1. Brush spots with wire brush.
  2. Add silver or copper algaecide to water and circulate. (these two can be done at the same time) Be careful to get all the algaecide in the water so it doesn’t stain the deck.
  3. Turn pump off and leave it off for 24 hours. Let the water settle so you can see every spot clearly.
  4. Apply chlorine directly to the algae spot. On floors this means spreading granular trichlor over the spot To do this I use a cup with a handle like a measuring cup. I fling my arm so that some of the granules fly away from me and over the water. I adjust my fling and my position so that I get a treatment onto the black algae directly on the spots. I do one fling at a time watching for it to land and adjusting my position and swing until I get all the spots. Don’t let a bunch pile up. It’s acidic and a pile might yellow the surface in that spot. If it’s on the walls rub a chlorine tab directly onto the spot. Wear gloves or get the tool that attaches a tab to the end of a pool pole and do it that way.
  5. leave it alone overnight.
  6. Brush, start pump, let cleaner run or vacuum the spot to get the dead algae off. backwash or clean the filters.
  7. If there are still some black algae spots, you should repeat the process. Only add copper or silver every 3-4 months. It will stain your pool.
  8. After vacuuming start filter pump for circulation and adjust pH. Keep your pool chlorine level adjusted to 7.2-7.6 to prevent re-occurrence. Keep your chlorine residual at 1.0-3.0ppm.
  9. Brush the walls and every surface weekly. Run your cleaner enough to keep the floor clean.
  10. Enjoy your pool. If spots reoccur treat again. Only add

Black algae spots occur in a swimming pool when your water has low free chlorine level and/or the pool chemicals are unbalanced. Good circulation is a must! The time took to avoid black algae is well worth your time and energy.