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How to Prevent and Treat Pool Stains

Identify common pool stains and effective removal methods

Nothing spoils the look of a sparkling blue pool faster than unsightly stains on the walls or floor. Whether you're a new pool owner or a seasoned pro, stains can be frustrating—but the good news is most are preventable and treatable. Let's break down the most common types of pool stains, how to identify them, and proven ways to remove and prevent them.

Types of Common Pool Stains

1. Organic Stains

What they look like:

• Green, brown, or sometimes reddish stains
• Irregular shapes, often found near where leaves, berries, or other natural debris settle

Causes:

• Leaves, twigs, berries, algae, or other plant material decomposing in the pool

2. Metal Stains

What they look like:

• Blue, green, black, reddish-brown, or rusty colored spots
• May appear as streaks, spots, or overall discoloration

Causes:

• Metals like iron, copper, or manganese entering the water (from source water, old pipes, pool equipment, or algaecides)

3. Scale and Mineral Stains

What they look like:

• White, gray, or sometimes brown crusty deposits along the waterline or pool surfaces

Causes:

• Hard water (high calcium or mineral content)
• Imbalanced water chemistry, especially high pH or calcium hardness

4. Rust Stains

What they look like:

• Small, dark brown or orange spots, often near metal objects (like ladders or screws)

Causes:

• Corroding metal parts, rebar, or debris left in the pool

How to Identify the Stain Type

• Organic stains can often be scrubbed off or fade with chlorine shock.
• Metal stains don't budge with scrubbing or shock and may change color when you rub with a vitamin C tablet (ascorbic acid).
• Scale/mineral stains feel rough or crusty to the touch.
• Rust stains are usually localized near metal fixtures or where metal has fallen in.

How to Remove Pool Stains

Organic Stains

Removal Steps:

1. Brush the area with a pool brush.
2. Shock the pool with a high dose of chlorine to oxidize organic material.
3. Run the filter for 24–48 hours.
4. Repeat if needed; stubborn stains may need a specialized enzyme cleaner.

Metal Stains

Removal Steps:

1. Test for metals using a pool test kit or strips.
2. Vitamin C test: Rub a vitamin C tablet on the stain—if it lightens, it's likely a metal stain.
3. Ascorbic acid treatment:
   • Lower chlorine to <1 ppm and pH to 7.2.
   • Sprinkle ascorbic acid directly on the stain or circulate in the pool.
   • Stain should fade within minutes to hours.
4. Add a metal sequestrant to bind metals and prevent redepositing.
5. Filter and vacuum thoroughly.

Scale and Mineral Stains

Removal Steps:

1. Lower water hardness and pH (aim for pH 7.2–7.4, calcium hardness 200–400 ppm).
2. Scrub the stains with a pumice stone or specialized scale remover.
3. Use a descaler or stain remover formulated for calcium and minerals.
4. Regularly brush and maintain balanced water chemistry.

Rust Stains

Removal Steps:

1. Identify and remove the metal source (old screws, toys, etc.).
2. Spot-treat with a vitamin C tablet or a commercial rust remover.
3. For persistent stains, use a stain eraser or ascorbic acid treatment as above.

How to Prevent Pool Stains

• Keep the pool clean: Skim debris daily and vacuum weekly.
• Maintain balanced water chemistry: Monitor pH, alkalinity, and calcium hardness; test for metals if you notice discoloration.
• Shock after storms or heavy use: This helps oxidize organic matter before it stains.
• Use a metal sequestrant: Especially if your water source is high in metals.
• Inspect and maintain equipment: Replace rusty parts and avoid using metal objects in the pool.
• Address scale early: If you notice white deposits, adjust your water chemistry right away.

Final Thoughts

Pool stains are common, but with the right knowledge, you can keep your pool looking pristine all season long. Regular maintenance, balanced water, and prompt stain treatment are your best defenses. When in doubt, consult a pool professional for stubborn or mysterious stains.

Enjoy your sparkling, stain-free pool—and happy swimming!

Have you battled pool stains before? Share your tips or questions in the comments!