Why Is My Pool Green? Common Causes and How to Fix It

Nothing ruins pool time faster than murky green water. Whether it’s a slight tint or a full-blown algae swamp, a green pool isn’t just an eyesore—it’s a warning sign that something’s off in your water chemistry or filtration system.

At Pool Service Cowboys, we’ve helped dozens of homeowners in Richardson and surrounding areas recover their pools after algae takes hold. Here’s what you need to know about the causes—and how to fix it.

What Causes a Pool to Turn Green?

1. Algae Growth (Most Common)

The number one reason your pool is green? Algae. It thrives in warm water, especially when chlorine levels drop. Algae can bloom in a matter of days, especially after heavy rain, heatwaves, or equipment failure.

2. Poor Circulation

Even if your chlorine is balanced, it won’t work properly without movement. If your pump or filter isn’t running long enough—or is malfunctioning—algae will find dead spots and grow fast.

3. Low or No Sanitizer

Chlorine kills algae. When sanitizer levels fall below safe thresholds (often under 1.0 ppm), you’ve got an open invitation for algae to bloom.

4. Filtration Problems

Clogged filters, worn-out cartridges, or poor backwashing can leave debris and organics in the water, feeding algae and reducing clarity.

5. Imbalanced Water Chemistry

High pH, low alkalinity, or elevated phosphates can weaken your sanitizer and create ideal conditions for algae.

What Type of Algae Is in My Pool?

There’s more than one type of green…

• Green Algae: Most common and easiest to treat. Causes cloudy or green-tinted water.
  
  
• Yellow (Mustard) Algae: Sticks to walls, tough to brush off. More stubborn.
  
  
• Black Algae: Appears as dark spots on plaster. Very tough to remove—requires aggressive treatment and brushing.
  
  

How to Fix a Green Pool (The Right Way)

Step 1: Test and Balance the Water

Adjust pH and alkalinity first. This ensures your chlorine shock will be effective.

Step 2: Shock the Pool

Use a high dose of chlorine (or a specialized algaecide) to kill the algae. This may take multiple rounds depending on severity.

Step 3: Brush All Surfaces Thoroughly

Algae clings to walls and ladders. Brushing dislodges it so your chemicals can do their job.

Step 4: Run the Filter 24/7

Continuous circulation helps remove dead algae and prevent it from settling again.

Step 5: Clean the Filter

After treatment, clean or backwash your filter to remove dead algae and debris.

When to Call a Pro

If your pool is more swamp than swim, save yourself the time (and guesswork). Our Green-to-Clean service includes:

• Same-week scheduling
  
  
• Certified chemical treatment
  
  
• Daily follow-ups until clear
  
  
• Final water balancing and filter care
  
  
• Before-and-after Skimmer reports
  
  

We’ve brought pools back from deep green, dark brown, and everything in between.

Need Help With a Green Pool in Richardson?

Don’t stress—Pool Service Cowboys is here to help. We’ll assess your pool, give you a clear plan, and bring your water back to crystal clear.