Understanding and Treating Organic and Inorganic Stains in Swimming Pools

Organic vs. Inorganic Stains: What's the Difference?

Organic Stains

• Source: Derived from living organisms such as algae, leaves, berries, or other organic debris.
• Characteristics: Typically easier to remove than inorganic stains because they are surface-level and don’t chemically bond with the pool material.
• Common Causes: Leaves falling into the pool, algae blooms, or organic matter like pollen or grass.
• Appearance: Often green, brown, yellow, or black, and may look patchy or irregular.

Inorganic Stains

• Source: Caused by metals or minerals in the water, such as iron, copper, manganese, or calcium.
• Characteristics: These stains are more stubborn as they chemically interact with the pool surface, often penetrating deeper into porous materials like plaster.
• Common Causes: Well water with high metal content, corrosion of pool equipment, or improper chemical balance.
• Appearance: Typically metallic-looking with colors like rust-red, blue-green, purple, or gray.

Identifying Stains by Color

Stain color is a key clue to their origin, though overlap between organic and inorganic stains can occur. Below is a guide to common stain colors and their likely causes:

Color	Likely Cause	Type
Green	Algae, leaves, or copper	Organic/Inorganic
Brown/Yellow	Leaves, dirt, or iron	Organic/Inorganic
Black	Black algae or manganese	Organic/Inorganic
Blue-Green	Copper	Inorganic
Red/Rust	Iron	Inorganic
Purple/Gray	Manganese	Inorganic
White/Gray	Calcium scale	Inorganic

Testing for Stain Type

To confirm whether a stain is organic or inorganic, simple tests can be performed:

1. Vitamin C (Ascorbic Acid) Test (Inorganic)

• How: Place a vitamin C tablet on the stain for 30 seconds, then check for lightening or removal.
• Result: If the stain fades, it’s likely inorganic (metal-based, e.g., iron or copper). Organic stains won’t react.
• Note: This test works best on plaster or fiberglass surfaces.

2. Chlorine Tablet Test (Organic)

• How: Place a chlorine tablet or sprinkle granular chlorine on the stain and wait 1–2 minutes.
• Result: If the stain bleaches or lightens, it’s likely organic (e.g., algae or leaf stains). Inorganic stains remain unaffected.
• Note: Avoid prolonged contact on vinyl liners to prevent bleaching.

3. pH and Metal Testing (Inorganic)

• How: Use a pool test kit to check for metals (iron, copper, manganese) in the water and measure pH/alkalinity.
• Result: High metal levels or imbalanced pH suggest inorganic stains. Organic stains don’t correlate with metal content.
• Tools: Metal test strips or liquid test kits (available at pool supply stores).

Treating Organic Stains

Organic stains are generally easier to treat because they respond well to chemical treatments and brushing. Below are methods tailored to each pool type:

Plaster/Gunite Pools

• Step 1: Brush the stain vigorously with a stiff nylon brush to loosen organic material.
• Step 2: Shock the pool with chlorine (raise free chlorine to 10–20 ppm) to kill algae or bleach organic matter.
• Step 3: Apply an algaecide if algae is suspected, following product instructions.
• Step 4: Run the filter for 24–48 hours and vacuum debris.
• Note: For stubborn black algae, use a stainless steel brush and consider a specialty algaecide.

Vinyl Liner Pools

• Step 1: Gently brush the stain with a soft nylon brush to avoid damaging the liner.
• Step 2: Shock the pool with chlorine (10–20 ppm) and add algaecide if needed.
• Step 3: Run the filter and vacuum debris carefully to avoid liner abrasion.
• Note: Avoid abrasive brushes or high chlorine concentrations for extended periods to prevent liner fading.

Fiberglass Pools

• Step 1: Brush the stain with a soft nylon brush designed for fiberglass surfaces.
• Step 2: Shock the pool with chlorine (10–20 ppm) and apply algaecide if algae is present.
• Step 3: Run the filter for 24 hours and vacuum debris.
• Note: Fiberglass is less porous, so organic stains are usually surface-level and easier to remove.

Pool enzymes can also be effective in treating many organic stains.  Follow instructions on the label which may include a slight increase for chlorine but not levels considered to be superchlorination/shock levels.  This could be considered for vinyl liner surfaces which are susceptible for fading with high chlorine levels.

Treating Inorganic Stains

Inorganic stains require targeted treatments to address metal or mineral deposits. Sequestering agents and acid treatments are often used, but care must be taken to avoid surface damage.

Plaster/Gunite Pools

• Iron/Copper Stains:
• Step 1: Lower pH to 7.0–7.2 to prevent further metal precipitation.
• Step 2a: Add a metal sequestrant (e.g., Jack’s Magic or Metal Free) per product instructions - or
• Step 2b: Apply ascorbic acid (vitamin C powder or a stain remover like Stain Free) directly to stains, brushing gently.
• Step 3: Run the filter for 24–48 hours and rebalance water chemistry.
• Manganese Stains:
• Step 1: Use a specialty manganese remover or ascorbic acid-based product.
• Step 2: Add a sequestrant to prevent recurrence.
• Calcium Scale:
• Step 1: Lower pH to 7.0 and use a scale remover (e.g., muriatic acid diluted per instructions).
• Step 2: Brush affected areas and vacuum debris.
• Note: Acid washing may be needed for severe stains but should be done by professionals to avoid etching.

Vinyl Liner Pools

• Iron/Copper Stains:
• Step 1: Lower pH to 7.0–7.2 and add a sequestrant.
• Step 2: Apply ascorbic acid-based stain remover with a soft cloth or sponge, avoiding abrasive brushes.
• Step 3: Run the filter and rebalance chemistry.
• Manganese Stains:
• Step 1: Use a manganese-specific remover and sequestrant.
• Step 2: Wipe stains gently with a soft cloth.
• Calcium Scale:
• Step 1: Use a vinyl-safe scale remover and wipe with a soft sponge.
• Step 2: Maintain balanced water chemistry to prevent recurrence.
• Note: Avoid acid washing or harsh chemicals, as they can damage vinyl liners.

Fiberglass Pools

• Iron/Copper Stains:
• Step 1: Lower pH to 7.0–7.2 and add a sequestrant.
• Step 2: Apply ascorbic acid-based stain remover with a soft sponge or cloth.
• Step 3: Run the filter and rebalance chemistry.
• Manganese Stains:
• Step 1: Use a manganese remover and sequestrant, applying with a soft cloth.
• Calcium Scale:
• Step 1: Use a fiberglass-safe scale remover and wipe with a soft sponge.
• Step 2: Brush gently and vacuum debris.
• Note: Fiberglass surfaces are non-porous, making stain removal easier, but avoid abrasive tools to prevent scratching.

Preventing Stains in Swimming Pools

Prevention is key to keeping your pool stain-free. Follow these tips for all pool types:

• Maintain Water Chemistry: Keep pH (7.2–7.6), alkalinity (80–120 ppm), and calcium hardness (200–400 ppm) balanced.
• Test for Metals: If using well water or noticing discoloration, test for metals and use a sequestrant regularly.
• Clean Regularly: Brush and vacuum the pool weekly to remove organic debris before it stains.
• Use a Pool Cover: Reduce organic debris like leaves and pollen.
• Monitor Equipment: Check for corrosion in heaters, ladders, or pipes that may introduce metals.

Key Considerations by Pool Type

• Plaster/Gunite: Porous surfaces are prone to deep staining, especially inorganic. Acid washing may be needed for severe cases but risks surface damage.
• Vinyl Liner: Non-porous but delicate; avoid harsh chemicals or abrasive brushes to prevent fading or tearing.
• Fiberglass: Non-porous and resistant to staining, but scratches from abrasive tools can worsen appearance.

Considerations for Ionized Pools

If you have an ionized pool, the treatments listed above should not be used.  Regardless of stain type pool surface, they should be treated differentially.  Speak with the manufacturer of the system you own and they can walk you through the process so not to remove the active ions used for sanitation.

Conclusion

Organic and inorganic stains in swimming pools require different approaches for identification and treatment. By using color cues, simple tests like the vitamin C or chlorine test, and tailored treatments for plaster/gunite, vinyl liner, or fiberglass pools, you can restore your pool’s pristine appearance. Regular maintenance and water testing are essential to prevent stains from recurring. For persistent or severe stains, consult a pool professional to avoid damaging your pool surface.

Keep your pool sparkling clean, and dive into a stain-free summer!

Note: Always follow product instructions and safety guidelines when handling pool chemicals. Test treatments on a small area first, especially on vinyl or fiberglass surfaces.