How To Remove Algae Stains From Pool Walls

It’s been a long cold winter, my concrete in-ground pool spent most of the last 4 months sitting with no cover and is completely algae-stained black and green and I must open it for Memorial Day.  How do you remove algae stains from a concrete pool?

  • Pump pool out
  • Clean debris-make sure all organic material is cleaned out
  • Apply Muriatic Acid/Water Solution 50/50 with a watering to Jug walls/floor
  • Start at the deep end and work up & out of the pool
  • Rinse off completely
  • Pump rinse out
  • Fill Pool-Balance Chemistry
  • Shock add Algaecide & Clarifier-Run Filter

For the longest time, the cover on our old pool lasted through some big snowstorms. This year, it gave in. I know what to expect when I pump the water out of the pool. A Green, Black murky swamp that just last season we were swimming in.

How To Remove Algae Stains From Pool Walls

Removing algae stains from pool walls requires a combination of thorough cleaning and treatment. Start by brushing the affected areas with a stiff-bristled brush to loosen the algae and expose it to treatment. It’s important to remove all organic materials like tree branches and leaves that will continue to stain the inside of the pool walls and floor. I use a Muriatic and water mix that when applied right will strip any stains that developed over the winter.

Follow the manufacturer’s instructions for proper application and dosage. After treating the stains, continue brushing and scrubbing the walls to dislodge any remaining algae and promote thorough cleaning.

For stubborn stains, consider using a pool-specific stain remover or an acid wash, but use these products with caution to avoid damaging the pool surfaces. Finally, ensure proper circulation and filtration to maintain water quality and prevent algae from returning. Regular maintenance, including brushing, skimming, and maintaining proper chemical balance, is key to preventing algae stains and keeping your pool walls clean and clear. Follow the steps in this article to bring your concrete in-ground pool back to its luster and beauty.

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Muriatic Acid Wash Before & After

Causes of Pool Stains

Pool stains can detract from the aesthetic appeal of your pool and indicate underlying issues that need attention. Understanding the various causes of pool stains is crucial for effective maintenance and prevention strategies. Stains in pools can result from a variety of factors, including:

Cause Description
Metals Metals such as iron, copper, and manganese can leach into the pool water from various sources, including
fill water, pool equipment, and algaecides. These metals can oxidize and form unsightly stains on pool surfaces.
Organic Matter Leaves, twigs, and other organic debris that find their way into the pool can decompose and leave behind stains.
Additionally, algae growth, if not promptly addressed, can lead to stubborn green or black stains.
Calcium Deposits Hard water with high calcium levels can cause calcium deposits to form on pool surfaces, especially in areas with
poor water circulation or around pool fixtures. These deposits can appear as white, chalky stains.
Chemical Imbalance Improperly balanced pool water, with high or low pH levels, alkalinity, or calcium hardness, can lead to
staining. pH levels that are too high can cause scaling, while low pH levels can corrode pool surfaces and
equipment, leading to metal stains.
Environmental Factors Environmental factors such as sunlight, rain, and wind-blown debris can contribute to pool staining over time.
Sunlight can accelerate chemical reactions that lead to stains, while rainwater can introduce contaminants
into the pool. Wind-blown debris, such as dirt and pollen, can also settle on pool surfaces and cause staining.

By identifying the specific cause of pool stains, pool owners can implement targeted maintenance strategies to prevent staining and keep their pools looking clean and inviting. Regular testing of water chemistry, routine cleaning and maintenance, and the use of appropriate chemicals and filtration systems are essential components of a comprehensive pool care regimen.

Pump Pool Water Out of the Swimming Pool

Remove the branches, leaves, and trash that are floating on top and at the bottom of the pool. Start where you can see. Work in a grid across the bottom of the pool and get everything. The more you get out the more you’ll save on the use of chemicals in the next process.

  • Open the pool Inlet Covers and blow any debris that is in the boxes into the pool. Make sure they are clean. Put the baskets back in and the Covers back on.
  • Clean the inside of the pool first. Make sure you collect and remove any Organic material that is unseen at the bottom of the pool.
  • Use a Soft Plastic Rake or a Leaf Bagger

If you leave any organic matter in the pool that material, no matter how small, will suck up the chemical’s active ingredients you are using and will triple the cost and amount you are using.  After you are done with cleaning the debris from the pool it’s time to clean the mess that is around the pool.

If you let it go,  as soon as the weather warms a few degrees, that organic material that you left from cleaning the inside of the pool will dry and stain your walkway or patio blocks that surround the pool area. Those new stains will be harder to remove than the stains you fight on the inside of your pool. So Get to it.

The equipment you’ll need:

  • A trash pump this size is Capable of moving up to 400 GPM of pool water and solids up to 1.5″ from pools. It can be rented for 4 hours at a time or the whole weekend.  While you are there pick up a Plastic Gardening watering can.
  • Watering Can-2 1/5 gallon watering can be used with the Muriatic Acid.
  • Eye Protection-protect you from Chemical Splash- You will need these. For a couple of dollars, you can save yourself from blindness by buying them,
  • Chemical Gloves-Versatile chemical protection gloves for when you need to be protected from hazardous materials. Made of a high-performance nitrile compound that provides an outstanding combination of chemical resistance and strength.

Is Your Empty Inground Pool a Confined Space

Whether an empty inground pool constitutes a confined space depends on various factors, including its design, size, and accessibility. Generally, a confined space is defined as an area that is large enough for a person to enter, has limited or restricted means of entry or exit, and is not designed for continuous occupancy.

In the case of an empty inground pool:

  1. Size and Design: If the pool is large enough for a person to enter and has limited means of entry or exit, such as a ladder or narrow access point, it may meet the criteria of a confined space.
  2. Accessibility: If the pool is empty and there are no obstructions or hazards inside, it may not be considered a confined space. However, if there are barriers, debris, or other obstacles that could impede entry or exit, it could be classified as such.
  3. Atmospheric Conditions: Even if the pool is empty, atmospheric conditions within the space can change and pose risks to anyone entering, such as the presence of toxic gases or lack of oxygen. Therefore, it’s essential to assess atmospheric conditions before entering any enclosed space, including an empty inground pool.

In summary, while an empty inground pool may not always be considered a confined space, it’s crucial to evaluate its specific characteristics and potential hazards before entering. Always prioritize safety and take necessary precautions to mitigate risks associated with confined spaces.

Remove Algae Stains in Concrete Swimming Pool

How to Acid Wash a Swimming Pool: 7 Steps (with Pictures)
Apply Acid Solution with a Watering Jug

Removing algae stains from a concrete swimming pool can be a challenging task, but with the right approach and products, you can effectively eliminate them. Here’s a list of steps to remove algae stains from a concrete pool:

  1. Brushing: Use a stiff-bristled brush or pool brush to scrub the affected areas vigorously. This helps loosen the algae from the surface of the concrete.
  2. Shock Treatment: Increase the chlorine levels in the pool water with a shock treatment to kill any remaining algae and prevent further growth. Follow the manufacturer’s instructions for the proper dosage.
  3. Algaecide: Apply an algaecide specifically designed for use in concrete pools. Choose an algaecide that targets the type of algae present in your pool and follow the recommended application instructions.
  4. Scrubbing: If the stains persist after shock treatment and algaecide application, continue scrubbing the affected areas with the brush to further break down the algae and remove stubborn stains.
  5. Acid Wash: In severe cases where algae stains are deeply embedded in the concrete, consider using an acid wash. Dilute muriatic acid in water according to the manufacturer’s instructions and apply it to the stained areas. Allow the acid to sit for a short period, then scrub the area again and rinse thoroughly with water.
  6. Pressure Washing: Use a pressure washer with a suitable nozzle attachment to power wash the entire pool surface, focusing on areas with algae stains. Be cautious not to use too much pressure, as it can damage the concrete surface.
  7. Repeat if Necessary: Depending on the severity of the algae stains, you may need to repeat the above steps multiple times to completely eradicate the algae and remove the stains.
  8. Preventive Measures: Once the algae stains are removed, take preventive measures to avoid future algae growth. Maintain proper water chemistry, regularly clean and brush the pool surfaces, and ensure adequate circulation and filtration to minimize the risk of algae infestation.

By following these steps and using appropriate products and techniques, you can successfully remove algae stains from a concrete swimming pool and restore its appearance.

Muriatic Acid Cleaning Solution

Muriatic Acid– is a serious stain remover. This chemical will clean pool stains from the walls and the floor of the swimming pool. The less expensive Muriatic Acid has more fumes and is more dangerous to handle. I have been using Muriatic acid for years always with great results for healthy water pools.

Directions for working on how to get rid of algae with Muriatic Acid:

  • Wear acid-resistant protective clothing, rubber gloves, and plastic safety glasses while using. To etch or clean concrete and masonry or metal:
  • Dilute to desired strength by adding acid carefully to water, and avoid splashing.
  • Start with a highly diluted mixture and strengthen gradually (1 part acid to 20 parts water).
  • Apply solution. Bubbling indicates the solution is strong enough to remove algae
  • Flush thoroughly with clean water immediately after cleaning or etching is complete.

Masonry can be very alkaline, which makes for poor adhesion of paints, etc. Washing masonry with muriatic acid neutralizes the alkalinity, leaving it in optimal condition to accept paints and other coatings. When cleaning masonry with muriatic acid, a powdery residue is left on the surface. Once that residue is rinsed off, you are left with a very clean, coating-friendly surface.

Acid Wash Algae Stains to Clean Pool Walls & Floor

Steps: Muriatic Acid For Algae Pool Cleaning:

Draining your inground pool after losing your cover and leaving the water exposed to the elements all winter is the Best Choice for a pool owner to make. It gives the pool owner the access and opportunity to get inside the pool and get things going.

You make valuable inspections that may be urgent and need your attention. Once the water is out you can see what’s on the bottom, and assess the damages that have happened over the winter. You can get an idea of other damage that you might have not known about. Cracks caused by stress or problems with the drain plug cover are important things, that if not addressed will get worse.

Acid wash pool surfaces without draining the pool | Trust the experts
Always  use a Respirator, Gloves & Protective Equipment

You’ll also be able to see if water from the outside yard is making its way in. That is a disaster waiting to happen. You can get the water out as fast as possible so you can get down to the real work, cleaning the algae stains and organic material stains that have to come out so you can get your pool back to the same place it was last season.

  • After the pool is pumped completely as far as it can go and all organic material is removed shut down the garden hose.
  • Remove any tools like the wheelbarrow rakes or pool leaf Baskets. All that is left is green and black algae-stained walls and bottom.
  • Let the walls in the pool dry a little more. This will give the Muriatic chemical a better activation when you ally it to the walls.
  • Keep the garden hose connected where you can get to it just in case you have a problem with splashing the Muriatic Acid on your skin. Always use this chemical safely. Muriatic Acid
  • Always wear Gloves and Protective Chemical-rated gloves. Use your brain and this stuff really will work!!
  • Always Add Acid to Water/never Water to Acid
  • Fill the Watering/Springling Can up with 2 parts water and 1 part Muriatic Acid.
  • Stay on the edge of the pool with the wind at your back (this will keep any fumes away from you) Walk the perimeter of the pool using the diluted Chemical in the Sprinkling Can and pour the solution at the top of the wall. It will cover the whole wall from top to bottom covering it.

Gases from Chlorine, Bleach, Cleaners, Epoxy or Rubber Base Pool Paint Muriatic Acid, and other chemicals found in Pool Supplies can react with water or humidity (which is water in the air) and change to a gaseous form that is heavier than oxygen. Vapor or gas sinks and pushes the oxygen up leaving you in a dangerous position. When you use products like pool chemicals be careful. After the pool is emptied cleaned and acid-washed it’s time to refill it and put the pump and filtering system back together.

  • Start at the deep end and work your way out of the pool
  • It will turn a yellowish color foam and smell pungent like vinegar. If it doesn’t foam and turn yellow it is not strong enough. Try a stronger dilution like 1 to 1.  Always pour Acid into Water Never Water into Acid. It’s just a little safer rule of thumb. That goes for any type of Acid.
  • Assuming that the Acid turns the algae yellow, move around the parameter of the pool, soaking the wall from the top and covering the entire area. Leave it to sit until you can noticeably see that the foaming has stopped and the acid is no longer activating on the wall. Then take the hose and rinse the Muriatic Acid from the wall and whatever rolled across the bottom towards the drain in the deep end. You can add more of the acid to troubled spots on the bottom of the pool using full strength.
  • Do Not Go In The Pool While You Are Using Muriatic Acid To Clean The Stains on The Pool Walls Or On the Pool Bottom. Even though the new Muriatic Acid is of lesser strength than the older stuff that I used, working in Water Treatment facilities, It’s still acid. It still reacts with water to form a gas that you can see in the air. It will still react with Humidity in the air. So using it needs to be done with caution. Like chlorine, it can take your breath away. If you are in a Confined Space, which is a space that is over your head like the deep end of a swimming pool, you are in a hole.

One question I always had was how often you should drain your inground pool-for more information on this and other questions stay here on MyWaterEarth&Sky-Keeping the water in your pool clean over the winter and covered up keeps the amount of work and money you will spend in the spring down considerably. Sooner or………………………….Continue reading

JimGalloway Author/Editor


  1. What causes algae stains in concrete swimming pools? Algae stains in concrete pools are typically caused by the growth and accumulation of algae on the pool surfaces. Factors such as poor water circulation, inadequate sanitation, and environmental conditions conducive to algae growth can contribute to the formation of algae stains.
  2. How do I know if my pool stains are caused by algae? Algae stains in concrete pools often appear as green or dark-colored patches on the pool surface. These stains may feel slimy to the touch and can be difficult to remove through regular brushing and cleaning.
  3. What is the best way to remove algae stains from a concrete pool? The most effective method for removing algae stains from a concrete pool involves a combination of brushing, shock treatment, algaecide application, and, in severe cases, acid washing. It’s important to follow proper safety precautions and use appropriate products and techniques to ensure successful stain removal.
  4. Can I use household bleach to remove algae stains from my concrete pool? While household bleach may help lighten algae stains temporarily, it’s not recommended as a primary solution for removing stains from concrete pools. Bleach can be harsh on pool surfaces and may cause damage or discoloration if not used properly. It’s best to use products specifically designed for pool maintenance and stain removal.
  5. How long does it take to remove algae stains from a concrete pool? The time it takes to remove algae stains from a concrete pool can vary depending on the severity of the stains and the effectiveness of the removal methods used. In some cases, stains may be removed after one treatment, while more stubborn stains may require multiple treatments over several days or weeks.
  6. How can I prevent algae stains from recurring in my concrete pool? To prevent algae stains from recurring, maintain proper water chemistry, ensure adequate circulation and filtration, regularly clean and brush the pool surfaces, and use algaecides as needed to inhibit algae growth. Additionally, addressing any underlying issues contributing to algae growth, such as poor sanitation or environmental factors, can help prevent stains from returning.
  7. Are algae stains in concrete pools harmful to swimmers?  While algae stains themselves are not harmful to swimmers, they can indicate poor water quality and sanitation, which may pose health risks. Algae growth can create slippery surfaces and provide a breeding ground for bacteria and other pathogens. It’s essential to promptly address algae stains and maintain proper pool maintenance to ensure a safe swimming environment.

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