How To Remove Pool Stains: Iron, Lime, Algae

Pool stains constitute an unappealing blemish that detracts from the pristine allure of a swimming pool. They primarily emerge due to imbalances in water chemistry, the presence of foreign materials, or the degradation of pool components. Moreover, they can be broadly classified into organic and inorganic categories.

The pool’s water chemistry plays an integral role in the manifestation of these stains. Acidic water, with a pH value below 7, can lead to etching on the pool surface, offering an ideal surface for stains to settle. In contrast, alkaline water with a pH above 7.8 can lead to scale formation, trapping dirt and minerals and thus leading to stubborn stains.

Foreign materials, both organic and inorganic, can also incite pool stains. Organic materials such as leaves, berries, and algae can release tannins that stain the pool, akin to how a tea bag would stain a white mug. Inorganic materials, such as metals like iron, copper, and manganese, can originate from the source water, corroded pool equipment, or even certain types of pool chemicals, resulting in colorful, hard-to-remove stains.

Moreover, the degradation of pool components can contribute to the staining. Corrosion of metal parts or the deterioration of pool surfaces can lead to the release of materials into the pool water, causing stains.

Here are some key points for identifying and removing pool stains:

1. Organic stains: These are caused by leaves, grass, insects, fruits, and other organic substances left in the pool for extended periods.
2. Inorganic stains: These are caused by well water with high iron content or incorrect pH levels leading to rust or limescale deposits.
3. Green spots: Most likely a result of green algae infestation, growing quickly and turning the pool green overnight if the water treatment is insufficient.
4. Black spots: Could be black algae or a high proportion of manganese and iron in the water appearing as black spots.
5. Reddish spots: Likely organic debris, possibly from nearby plants like blueberries or an excess of algaecide.
6. Yellow spots: Probably mustard algae, relatively rare but identifiable by the yellowish mustard color.
7. Pink spots: Not algae but bacteria, often making themselves noticeable through slippery surfaces.
8. Brown spots: Caused by a high proportion of manganese or iron in the pool, most commonly due to filling the pool with well water.
9. White spots: Likely deposits from flakes or bleach stains, easy to remove from the pool floor.

The key to maintaining a clean, stain-free pool is prevention. Regular testing and balancing of pool water, ensuring the filter system runs daily, and regularly cleaning the pool can prevent organic deposits. Testing for iron in pool water and maintaining optimal pH levels can prevent iron and rust stains.

Why Do Pool Stains Appear?

Pool stains appear primarily due to imbalances in water chemistry, the presence of foreign materials, or the breakdown of pool components.

Water chemistry plays a crucial role in the appearance of pool stains. When the pH level of your pool water is too high or too low, it can lead to staining.

• Acidic Water: When the water in your pool becomes too acidic (pH below 7), it can lead to etching on the pool surface. This etching can create rough spots that are prime real estate for stains to settle in. It’s like when you have a small cut on your skin, and it becomes a magnet for dirt and grime.
• Alkaline Water: On the other hand, if your pool water swings to the other end of the pH scale and becomes too alkaline (pH above 7.8), it can lead to scale formation. These scales can trap dirt and minerals, leading to stubborn stains. Imagine it like hard water stains on your glass shower doors – those are tough to get rid of, right?

Foreign Materials Can Cause Stains In Your Pool

Foreign materials, both organic and inorganic, can cause pool stains.

1. Organic Materials: Leaves, berries, algae, and other organic debris can leave stains if they’re allowed to settle and left too long on your pool surface. These materials can release tannins, which can stain your pool, much like how a tea bag would stain a white mug.
2. Inorganic Materials: Metals like iron, copper, and manganese can cause stains when they are present in your pool water. These metals can come from the source water, corroded pool equipment, or even from certain types of pool chemicals. These stains can be colorful and are often harder to remove. It’s like when you leave a penny in a cup of water for a while, and it leaves a greenish-blue stain.

Breakdown Of Pool Components Can Cause Stains In Your Pool

Finally, the breakdown of two pool components can also lead to pool stains.

1. Corrosion of Metal Parts: If you have metal ladders, railings, or other metal parts in your pool, corrosion can cause them to release metals into the pool water, leading to stains. It’s similar to how rust forms on a car.
2. Deterioration of Pool Surfaces: Over time, pool surfaces can deteriorate, leading to the release of plaster, cement, or other materials into the pool water. These materials can settle on the pool surface and cause stains.

How To Identify Stains On The Pool Surface?

There are two types of stains to identify in your swimming pool.

1. Organic stains: Leaves, grass, insects, fruits, etc., provide bacteria and algae with a source of nutrition and lead to stains in the pool when organic substances remain in the pool for a longer period.
2. Inorganic stains: Well water with a high iron content or an incorrect pH level lead to rust or limescale deposits in the pool.

The distinction is not trivial, as a suitable cleaning method and agent against pool stains should only be selected after being determined.

In the following chapters, you will find out how to identify different stains in your pool and what causes are responsible for the appearance of stains on the bottom and on the pool walls.

What Are Those Green Spots In Your Swimming Pool?

• Green algae infestation (organic)
• Slightly green to dark green in color

If you discover green spots in your pool, there is a high chance of green algae. You can recognize this type of algae by local growth in the corners and walls. The algae are initially light green and turn dark green over time.

Green algae grow quickly and turn your pool green overnight if the water treatment is poor and the filter run times are too short.

Storms with rain and humid air promote algae growth in your pool – despite optimal water levels. Fortunately, the green algae can be removed quickly – you can find the instructions below.

What Are Those Black Spots In Your Pool?

• Black algae infestation (organic)
• Dark spots on the floor and on the walls

If the black spots are isolated dots or large-scale deposits, this could be black algae (also known as blue algae).

You can check this by pouring some chlorine granules onto a small area in your pool. If the black color turns brown, then it is organic stains.

Another indication of black algae is that it is difficult to remove with a brush.

And how do these algae get into your pool?

Black algae are usually introduced into the pool through dirty bathing suits.

However, the black pool stains may be caused by a high proportion of manganese and iron in the water and appear as black spots.

Tip: If you discover black to dark blue stains on the pool liner, it is not necessarily the blue algae because this predominantly grows in concrete pools.

What Are Those Reddish Spots In Your Swimming Pool?

• Probably organic debris
• Reddish spots on the pool floor

Take a pool brush and see if the red stains come off easily. If so, then it is very likely that these stains are organic.

You may have blueberries growing nearby and causing stains in your swimming pool.

If there is too much algaecide, reddish-brown stains can form in your pool and cloud the water. In my blog post, I explain in detail how the algaecide works.

What Are Those Yellow Spots In The Swimming Pool?

• Mustard algae in the pool (organic)
• Local growth of algae or yellow border in the pool

Yellow algae in your pool are relatively rare, also known as mustard algae or golden algae.

You can recognize this type of algae by the yellowish mustard color. However, in the early stage, it can be confused with the green algae.

Most corners are infested first, and a yellow border forms in your pool.

The yellow algae probably get into your pool via a host like ducks, and other animals, or by pollen.

Ineffective disinfection of your pool water and short circulation times encourage mustard algae to grow in your swimming pool.

What Are Those Pink Spots In The Pool?

• Bacteria in the pool (organic)
• Pink stains in the pool and on the filter

Most pool owners speak about pink algae when they see pink or red spots in the pool. However, these are not algae but bacteria.

The bacteria cannot be visually recognized immediately because they are initially transparent. Typical pink-red stains appear in the pool only after using disinfectants like chlorine.

These bacteria (pink algae) often make themselves noticeable through slippery surfaces.

How the bacteria – or pink algae – arise is not clear.

But you should know that these pink spots in your pool are harmful to your health.

What Are Those Brown Spots In Your Pool?

• Manganese or iron deposits
• Extensive infestation in the pool

Brown spots and cloudiness are caused by a high proportion of manganese or iron in your pool. Mostly this is the case after filling the pool with well water.

However, it is also possible that rust falls into your pool from a nearby fence or other objects.

If there are no leaves in your pool, which causes the brown coating on the pool bottom, you can assume that the water has a high iron level.

What Are Those White Spots On The Pool Bottom?

• Deposits from flakes or bleach stains
• Easy to remove dirt on the floor

White spots on the pool floor are caused by flocculants that have not been filtered or incorrect use of chlorine tablets.

You can recognize the flakes because they can be easily swirled up.

In the case of white spots on the pool liner, chlorine spots (bleaching spots) can be assumed. If the stains are bleaching spots, you have to live with them.

The bleaching stains often occur in vinyl or PVC pools that are chlorinated using a floater (metering float).

How To Remove Pool Stains?

Identifying the spots in your pool and clearing up the cause is only half the job.

If you want a quick overview, the table shown will help you to learn how to remove pool stains.

Detailed instructions on how to remove inorganic and organic pool stains can be found in the next chapter.

How To Remove Organic Swimming Pool Stains?

The most common stains in the pool are organic and can be removed with five simple means.

1. Test and optimize the pool water: Use test strips to measure the current water levels ​​in the pool and optimize them if necessary. The pH level should be between 7.2 and 7.6, the alkalinity between 80 and 120 ppm, and the calcium hardness between 200 and 400 ppm.
2. Do a local pool shock: For small stains, sprinkle chlorine granulate locally on the floor, and for large stains, the pool should be completely sprinkled. Let the chlorine sit for 24 hours with the pump turned off.
3. Scrubbing the pool: After 24 hours, the pool must be cleaned with a pool brush.
4. Start the filter system: Let the pump run for 24 to 36 hours until the water becomes clear again and the chlorine level sinks below 1.5 ppm.
5. Check your pool: Are the stains gone? Perfect! Otherwise, repeat the process again.

A pool brush and the filter pump will often do the job to remove organic pool stains, but you have to take stricter measures in other cases.

You do not necessarily have to do a pool shock in the case of pool stains from leaves or light residues from green algae. But if you have to apply a shock cleaner, read through my instructions about the pool shock beforehand.

If there are stains on your pool wall, it is impossible to apply chlorine granules locally. In this case, you have to clean your pool differently.

1. Testing pool water: First, you have to test and adjust the water levels in the pool ​​- see above.
2. Use the pool brush: Before the shock chlorination starts, the deposits must be removed from the wall with a pool brush so that the chlorine works better.
3. Shock the pool: Now, use liquid chlorine and pour it into the nozzles of the return flow of the pump. Depending on the concentration, 5 – 10 liters of liquid chlorine per 25 m³ of water are sufficient.
4. Use flocculant: It is advisable to use a flocculant in addition to chlorine.
5. Let the pump run: Start the pump and run it for 24 – 36 hours – if necessary longer until the water clears again.

I recommend doing the pool shock late afternoon or in the evening. It is important to have the correct concentration of liquid chlorine to avoid an overdose in your pool.

How To Remove Limescale And Iron Deposits In Your Pool?

Stains caused by limescale or iron in your pool are more challenging to remove but not impossible.

Remove inorganic deposits such as lime in your pool with my seven steps instruction.

1. Switch off the pump: First, switch off the pool pump.
2. Put on protective equipment: It is essential to wear protective goggles and a protective mask for your own protection.
3. Remove slight limescale: Apply the hydrochloric acid (pH minus) to a sponge and wipe off the limescale from your pool liner.
4. Remove limescale in the filled pool: Pour the acid in the appropriate places in the pool and let the water rest for 1 day.
5. Scrubbing lime: After the acid has taken effect, first scrub the walls and then the floor.
6. Vacuum the pool: Finally, you have to vacuum the pool with a pool vacuum.
7. Optimize pH: Use pH-Plus to adjust the pH level. This should not exceed the limit of 7.6 – otherwise, lime will form again.

You need 5 to 10 liters of hydrochloric acid per 25 m³ of water to clean the lime in your pool. You should also measure and adjust the pH level after every rain.

Learn how to remove iron deposits and rust in your swimming pool in three steps.

1. Test the water: Test the pool water for the iron level using a suitable measuring method.
2. Buy a metal stain remover: If you know what kind of metallic stains occur in the pool, then you can buy a special pool stain remover.
3. Follow the instructions: Since every stain remover works differently, read the manufacturer’s instructions and follow the instructions.

Rust stains and other iron deposits should possibly be cleaned in the pool after the winter, even before the pool is filled.

How To Prevent Stains In Your Pool?

After the organic and iron deposits have been removed from your pool, preventive measures should be taken to prevent re-staining.

How To Prevent Organic Deposits In Your Pool?

Organic deposits in your pool water can be prevented with six tips. All you need is a pool cleaning routine.

1. Pay attention to the water balance – the pH level, total alkalinity, and calcium hardness – are correct.
2. Let the filter system run through daily for 6 – 8 hours and, if necessary, optimize the nozzles to prevent dead zones in the swimming pool. Add a flocculant when filtering.
3. Regularly clean the pool with the pool brush. Alternatively, you can use a pool robot against deposits.
4. Use a skimmer and a pool net to remove leaves, insects, etc., from the water surface so that they do not end up on the ground.
5. Remove plants that bear fruit and fall into the pool.
6. Regularly check for stains in the pool, and don’t wait long to clean the pool.

Also rinse the filter monthly or clean the cartridge filter to prevent pool stains.

How To Prevent Iron And Rust Stains In Your Pool?

1. Regularly test the amount of iron in the pool water and use a flocculant to prevent it.
2. The pH level should not fall below 7.2 – otherwise, corrosion will quickly form in the pool. In addition, an optimal pH level favors the filtering off of iron.
3. Ensure that the pH does not rise above 7.6 – otherwise, limescale will build up in the pool.
4. Check all pipes in the pool for rust residues and other damage, such as scratches on steel wall pools. These parts may need to be repaired or replaced.
5. Change the filter sand annually if it is used too heavily.

Pool products against water clouding are not stain removers for rust. You can only bind the metal ions and prevent deposits.

If you have any further questions about pool maintenance, I recommend my helpful search function. Alternatively, you can write to me at on Twitter. I will help you personally.