Maintaining a crystal-clear swimming pool is a priority for every pool owner. However, over time, pool plaster—the most common surface type for concrete pools—can develop unsightly brown stains. These stains not only detract from your pool’s appearance but can also be a sign of underlying water chemistry or maintenance issues. The good news is that brown stains can typically be removed and prevented with the right strategies.
In this detailed guide, we’ll walk you through everything you need to know about identifying the causes of brown stains on pool plaster and the most effective methods to clean and prevent them. Whether you’re a seasoned pool owner or new to pool maintenance, you’ll find expert-backed solutions that are both practical and long-lasting.
Understanding the Causes of Brown Stains on Pool Plaster
Before diving into cleaning techniques, it’s essential to understand what causes brown stains. Identifying the root cause ensures that the solution you choose will be effective and that future stains can be avoided.
1. Metal Oxidation: The Most Common Culprit
Brown stains are often the result of metal oxidation. Pools with well water or those using untreated water sources may contain high levels of metals such as iron, manganese, or copper. These metals oxidize when exposed to chlorine, leading to discoloration on the plaster surface. Iron typically causes rust-colored stains, while manganese results in dark brown or black marks.
2. Organic Contaminants
Leaves, dirt, algae, and other organic matter can settle on the pool surface and create brown or tan stains. Especially after seasons like fall, when debris accumulates heavily in pools, these stains may become apparent.
3. Water Chemistry Imbalances
Improper pH, alkalinity, or calcium hardness levels can lead to corrosion of pool walls or the circulation system, which in turn can release metals and cause staining. Alternatively, unbalanced water can cause calcium scaling or etching, which changes the appearance of plaster and mimics staining.
4. Algae Accumulation
Although algae is traditionally associated with green stains, black algae and mustard algae can appear as brownish discolorations. These algae can attach to pool plaster and are resistant to normal chlorine levels, requiring aggressive treatment.
Preparing for Stain Removal
Before trying to remove the stains, it’s important to assess your pool’s condition and gather the necessary tools and chemicals. This preparation ensures the cleaning process is both effective and safe for your pool surface.
Check Your Water Chemistry
Start by testing your pool water using a reliable test kit. Ensure all levels are balanced, including:
- **pH:** 7.4–7.6
- **Total Alkalinity:** 100–120 ppm
- **Calcium Hardness:** 200–400 ppm
- **Chlorine:** 1–3 ppm
If imbalances are found, correct them before proceeding with stain treatment.
Gather the Right Tools and Chemicals
Depending on the type of stain and severity, you may need the following:
| Item | Purpose |
|---|---|
| Ascorbic Acid | Treats metal stains |
| Soda Ash or Baking Soda | Used for oil-based or organic stains |
| Polyphosphate Pool Stain Remover | Effective for temporary stain removal |
| Non-metallic Pool Brush with a Stiff Brush Head | For scrubbing surface stains |
| Goggles, Gloves, and Mask | Protective gear during chemical handling |
Stain Identification: Is It Organic or Metallic?
Successful stain removal often depends on correctly diagnosing the type of stain. Here’s how to tell the difference:
Metallic Stain Test
Throw a few tablets of ascorbic acid (vitamin C) into the pool and let them float over the stained area. If the stain lightens or disappears, you’re dealing with a metal-related stain. If not, proceed to the next test.
Organic Stain Test
Add a few spoonfuls of soda ash or baking soda into a sock or mesh bag and suspend it over the stain. Alternatively, brush the area with a solution of baking soda and water. If the stain lifts, it’s an organic stain.
Removing Brown Stains from Pool Plaster
Now that you have identified the type of stain, you can proceed with the appropriate treatment strategy.
1. Treating Metallic Brown Stains
Metallic stains require a metal-specific approach. Ascorbic acid is often the most effective for treating existing stains, while metal sequestrants help prevent future problems.
Supplies Needed:
- Ascorbic Acid Powder
- Soft Bristle or Nylon Brush
- Protective Gear
Steps:
- Balance your water chemistry first. Ensure your pH is below 7.6 and alkalinity is within the recommended range
- Turn off the pool pump to prevent water circulation
- Prepare the ascorbic acid by mixing it with a small amount of water or applying it directly as a powder
- Apply the powder or paste directly to the stain
- Gently scrub the area with a soft-bristle brush
- Rinse the area by hand without disturbing the water flow too much
- Wait 24 hours and retest the water balance and stain disappearance
If the stain persists, repeat the process or consider draining and acid-washing the pool for severe cases.
2. Dealing with Organic Brown Stains
Organic stains usually respond well to chlorine or algaecide-based treatments. However, the most effective methods target the specific source—such as leaves or algae.
Step-by-Step Process:
- Brush the stained surface to loosen any debris or dirt buildup
- Super-chlorinate the pool by adding a large dose of chlorine to kill algae or bacteria
- Clean and vacuum the pool thoroughly after chlorinating
- For stubborn stains, mix a bucket of baking soda and water, apply it to the stain, wait 15–20 minutes, and scrub again
- Vacuum the remaining residue and run the filtration system to clear cloudy water
If you suspect mustard algae, use a quaternary ammonium algaecide to treat the issue and brush weekly to prevent recurrence.
3. Removing Persistent or Deep-Seated Stains
Deep stains may require more aggressive action:
Possible Treatments Include:
- Draining the pool and conducting an acid wash: This can strip metal buildup and restore the pool surface but should be done by a licensed professional due to the use of muriatic acid
- Applying a stain-dissolving chemical such as a polyphosphate solution; these encapsulate stain-causing molecules and allow them to be filtered out
- Using a sequestering agent; these bind metals in solution and prevent further staining
Preventing Brown Stains on Pool Plaster
Once you’ve successfully removed brown stains, the challenge becomes keeping them from returning. Prevention involves a holistic approach to pool water care.
1. Regular Water Testing and Balancing
Maintaining perfect water chemistry is the best defense against metal staining and surface discoloration. Test your water at least once a week and adjust as needed. For pools using well water, consider pre-filtration systems to remove high levels of iron and manganese.
2. Use Metal Sequestrants and Stain Preventatives
Many commercial products are designed to bind dissolved metals in your water, preventing oxidation and surface staining. These should be used regularly, particularly if you know your fill water contains metals.
3. Pool Cover for Downtime
If your pool is not in daily use, covering it prevents organic debris and sunlight-induced algae growth. A custom-fitted pool cover reduces maintenance and helps protect your plaster surface from stains.
4. Routine Brushing and Cleaning
Don’t wait for stains to appear. Brush the pool walls and floors weekly to dislodge any foreign matter. Daily skimming and vacuuming also prevent surface staining from debris build-up.
Choosing the Best Plaster Finish for Stain Resistance
Not all pool plaster surfaces are created equal. The type of plaster you have can affect how likely it is to stain.
Traditional White Plaster
White plaster is the most commonly used finish. While it’s affordable and classic, it also shows stains easily and may require frequent cleaning.
Colored or Aggregate Plaster
Finishes like quartz or pebble have larger aggregate materials that resist staining and show dirt less visibly. Pebble plaster adds durability and aesthetic appeal while reducing the appearance of small stains.
Epoxy and Tile Finishes
For maximum stain resistance, consider coatings like epoxy paint or tile liners, but keep in mind these come with higher cost and longer installation periods compared to traditional plaster.
Kids, Pets, and Stain Accumulation
Families with children or pets may experience faster staining due to oils, sunscreen, and dirt introduced into the pool. Establishing a rinse shower or foot bath routine can greatly reduce contaminant buildup. In addition, a regular regimen of stain preventatives becomes even more important in high-use pools.
Professional Help: When to Call a Pool Technician
If your brown stains don’t respond to DIY treatments or are widespread, it may be time to consult a professional pool technician. They have access to industrial-grade products, equipment like high-pressure cleaning jets, and specialized knowledge for long-lasting repairs.
Long-Term Pool Maintenance Strategies
To keep your pool free of brown stains, develop a proactive maintenance schedule:
Weekly Checklist
- Test water chemistry
- Brush all walls and floor
- Remove surface debris
- Check chemical feeders and ensure correct dosing
- Vacuum the pool if necessary
Monthly Checks
- Inspect all metal components in the pump and filter system for corrosion
- Deep clean return lines with a line-cleaning foam ball or algaecide
- Test for metals using a metal test kit
- Add sequestering agents if needed
Final Thoughts: Keep Your Pool Looking Its Best
Brown stains on pool plaster can be frustrating, but they’re not a death sentence to your pool’s aesthetics. With proper identification, the right cleaning tools, and a consistent maintenance routine, pool owners can keep their pools looking vibrant and clear all season long.
Remember, the key to stain-free plaster isn’t just a quick fix, it’s an ongoing commitment to balanced water chemistry, preventive care, and routine cleaning. Whether you choose to DIY or work with a professional, the effort will pay off in crystal-clear water and a surface that shines like new.
Now that you have a full picture of how to tackle brown stains, it’s time to roll up your sleeves, get organized, and bring your pool back to life.
What causes brown stains on pool plaster?
Brown stains on pool plaster are typically caused by the presence of metals in the water, such as iron, manganese, or copper. These metals can originate from various sources, including well water, corroded pool equipment, or even decorative rocks and soil that enters the pool. When the pool water is imbalanced or exposed to chlorine, these metals oxidize, creating unsightly brown or rust-colored stains on the plaster surface.
Additionally, organic matter like decomposing leaves, algae, or other debris may also contribute to brown discoloration if left sitting on the pool surface for extended periods. In some cases, a combination of metal content and organic material can worsen the staining. Understanding the source of the stain is crucial because treating metal stains versus organic stains often involves different procedures and chemicals.
How can I determine if the brown stain is due to metals or organic matter?
To identify the type of stain, you can perform a simple test using a vitamin C tablet or ascorbic acid. Drop the tablet or sprinkle some ascorbic acid directly onto the brown stain. If the stain lightens or disappears, it is likely caused by metals such as iron. Metal stains often respond well to ascorbic acid because it acts as a reducing agent that breaks down metal oxides.
For organic stains, use a small amount of chlorine or pool shock directly on the stain (using a sock or skimmer basket for controlled application). If the stain lightens or disappears within a few minutes, it is organic in nature. Distinguishing between metal and organic stains helps ensure you apply the correct treatment method, saving time and preventing damage to the plaster surface.
What chemicals do I need to remove metal-related brown stains from pool plaster?
To remove brown stains caused by metals like iron or manganese, you will typically need ascorbic acid or a commercial metal stain remover. Ascorbic acid works effectively to break down the oxidized metal compounds, while a store-bought stain remover usually contains specialized chemicals that chelate or bind with the metals, removing them from the surface. In addition, a stiff pool brush helps loosen the stain, and it’s important to have proper safety gear like gloves and goggles on hand.
You should also have access to a pH testing kit, as the water’s chemistry can affect the stain removal process. Ideally, the pH level should be slightly acidic (around 7.0 to 7.2) to enhance the effectiveness of the stain remover. Maintaining balanced water during and after the treatment helps prevent re-staining and protects the longevity of your pool plaster.
Can I use a pumice stone to remove brown stains from pool plaster?
Yes, a pumice stone can be used to remove some types of brown stains on pool plaster, but it should be done carefully. Pumice stones are abrasive and effective for removing mineral deposits and light stains, including some caused by metals or organic compounds. However, because they are rough, they can scratch or damage the pool plaster if not used gently or on an already weakened surface.
It’s best to test a small, inconspicuous area before using a pumice stone on visible stain spots. Always wet the stone and the plaster before scrubbing in circular motions. After using the pumice stone, thoroughly rinse the area and retest water chemistry to ensure balance. For best results and to minimize risk, it’s recommended to combine pumice stone scrubbing with appropriate stain removal chemicals and proper brushing techniques.
How long does it typically take to remove a brown stain from pool plaster?
The time required to remove a brown stain from pool plaster can vary depending on the severity of the stain, the method used, and the chemicals applied. For fresh or light stains, using ascorbic acid or a liquid stain remover may lift the discoloration within a few minutes of application with some brushing. More stubborn stains or deeply embedded metal stains might require repeated applications and longer contact time, sometimes up to 24 hours, to see significant results.
Patience is key, as aggressive scrubbing or rushing the process can damage the pool’s surface. Applying the product, brushing the area, and waiting the recommended period allows the chemical reactions to work effectively. If the stain persists after the first effort, it may be necessary to adjust the chemical balance of the water, use specialized sequestering agents, or consult with a pool professional to prevent further discoloration and protect the plaster.
How can I prevent brown stains from reappearing on my pool plaster?
Preventing brown stains requires regular maintenance and proactive measures. One of the most effective ways is maintaining proper water chemistry, including monitoring and controlling the metal content in your pool water. Using a sequestering agent regularly can help bind metals in the water and keep them from oxidizing and settling onto the plaster. Additionally, testing your source water during fill-ups or top-offs can help identify if high metal levels are being introduced.
Avoid allowing debris, leaves, and dirt to sit on the pool bottom or walls for extended periods. Regular brushing, cleaning, and vacuuming keep surfaces free of contaminants. It may also help to install a sacrificial anode (for metal staining) or use a metal filter system if your pool has recurring issues. Protecting the plaster finish and maintaining a consistent chemical balance are key to long-term pool aesthetics and surface integrity.
When should I consult a professional about brown stains in my pool?
If you’ve tried multiple stain removal techniques and the brown stains persist or reoccur despite your efforts, it may be time to consult a professional pool service. Persistent stains could indicate deeper issues, such as underlying plumbing corrosion, source water quality problems, or plaster deterioration that is beyond DIY remedy. Professional technicians have access to advanced testing tools, stronger stain-removal products, and the expertise needed to diagnose and resolve complex staining situations.
Additionally, if you’re uncertain about the type of stain or the correct approach for removing it without damaging your plaster, seeking expert advice before proceeding can save time and prevent costly mistakes. Pool professionals can also help establish a preventive maintenance plan tailored to your specific pool type and water conditions, ensuring a clean, attractive appearance year-round.