Why Is My Pool Water Turning Yellow?

Yellow water can indicate mustard algae or high levels of organic debris. Shock the pool and scrub thoroughly.

Common Causes of Yellow Pool Water

Several factors can turn your pool water yellow. Identifying the source will help you determine the best way to fix it.

1. Mustard Algae Growth

Mustard algae is one of the most common culprits behind yellow pool water. Unlike green algae, mustard algae appears as a yellow or brownish film on pool surfaces, often in shady areas.

How it happens:

• Poor circulation allows algae to settle and grow.
  

• Low chlorine levels make it easy for algae to thrive.
  

• Contaminated swimsuits or pool toys introduce algae spores.
  

2. High Iron Content

Metals in the water, particularly iron, can cause a yellow or brown tint. This often happens when filling a pool with well water or when corroded pipes release iron into the pool.

How to tell if it’s iron:

• The water turns yellow or brown after adding chlorine.
  

• Stains appear on pool walls or steps.
  

• A pool test kit detects high iron levels.
  

3. Pollen Accumulation

During certain seasons, pollen from trees and plants can settle on the water’s surface and cause a yellowish tint. While it may look like algae, pollen doesn’t cling to surfaces the same way.

How to check:

• The yellow substance floats on the surface.
  

• It does not stick to pool walls or steps.
  

• It’s more common in outdoor pools surrounded by trees.
  

4. Chemical Imbalance

If your pool’s pH, alkalinity, or sanitizer levels are off, the water can take on a yellow hue.

Common imbalances include:

• Low chlorine, allowing contaminants to build up.
  

• High pH causing minerals to discolor the water.
  

• Unbalanced alkalinity affecting water clarity.
  

How to Fix Yellow Pool Water

Once you identify the cause, you can take the right steps to clear up your pool water.

1. Treat Mustard Algae

If mustard algae is the issue, follow these steps:

• Brush and vacuum: Scrub all pool surfaces to remove algae buildup.
  

• Shock the pool: Use a high-dose chlorine shock to kill algae spores.
  

• Use an algaecide: Choose a product designed specifically for mustard algae.
  

• Run the filter: Keep it running continuously for at least 24 hours.
  

• Wash swimsuits and accessories: Rinse anything that has been in the pool to avoid recontamination.
  

2. Remove Iron from Pool Water

For pools with high iron levels:

• Use a metal sequestrant: This prevents metals from oxidizing and staining the pool.
  

• Add a metal filter: If you use well water, install a pre-filter to catch iron before it enters the pool.
  

• Shock carefully: If iron is present, use a lower-chlorine shock to avoid triggering yellow discoloration.
  

3. Remove Pollen

If pollen is causing the yellow tint:

• Skim the surface: Use a fine-mesh skimmer to remove pollen daily.
  

• Run the filter: Keep your pool’s circulation system running to catch fine particles.
  

• Use a clarifier: This helps clump pollen together so the filter can trap it more effectively.
  

4. Balance Pool Chemicals

If chemical imbalance is the issue:

• Test the water: Check chlorine, pH, and alkalinity levels with a test kit.
  

• Adjust chlorine: Maintain levels between 1-3 ppm for proper sanitation.
  

• Correct pH and alkalinity: Ideal pH is 7.4-7.6, and alkalinity should be between 80-120 ppm.
  

Preventing Yellow Pool Water

To keep your pool clear and prevent yellow water from returning, follow these maintenance tips:

• Maintain proper chlorine levels: Regularly check and adjust chlorine to prevent algae and bacteria growth.
  

• Keep your filter clean: Rinse or replace filters as needed to ensure good circulation.
  

• Skim and brush regularly: This prevents buildup of algae and pollen.
  

• Monitor metal levels: If using well water, test for metals and use a sequestrant if needed.
  

• Shock weekly: Regular shocking helps prevent algae and maintains water clarity.
  

By staying on top of pool maintenance, you can prevent yellow water from becoming a recurring issue and keep your pool looking clear and inviting all season long.