Why Is My Pool Green? 7 Common Causes & Quick Fixes

Quick Answer: Your pool is green because of algae growth, caused by low chlorine, poor circulation, imbalanced pH, or lack of cleaning. The fastest fix is to shock your pool with chlorine, brush thoroughly, and run your filter 24/7 until clear.

March 16, 2026 10 min read Project 36 Services

Table of Contents

  1. Cause #1: Low Chlorine Levels
  2. Cause #2: Poor Water Circulation
  3. Cause #3: Imbalanced pH Levels
  4. Cause #4: Lack of Regular Cleaning
  5. Cause #5: High Phosphate Levels
  6. Cause #6: Warm Weather
  7. Cause #7: Rain & Debris
  8. How to Fix a Green Pool in 5 Steps
  9. Prevention Tips

If you're staring at green pool water and wondering what went wrong, you're not alone. As Arlington's pool service experts with 21 years of experience, we've helped hundreds of homeowners fix their green pools. In this guide, we'll explain exactly why your pool turned green and how to restore crystal clear water.

Cause #1: Low Chlorine Levels (Most Common)

The #1 reason pools turn green is insufficient chlorine. Chlorine kills algae spores before they can multiply. When levels drop below 1 ppm (parts per million), algae can take hold and spread rapidly.

Ideal Chlorine Levels

  • Normal: 1-3 ppm
  • Low (Risk Zone): Below 1 ppm
  • Shock Level: 5-10 ppm for treatment

Cause #2: Poor Water Circulation

Stagnant water is algae's best friend. Your pool pump should run 8-12 hours daily during summer to circulate chemicals and filter debris. Poor circulation creates "dead zones" where algae thrives.

Cause #3: Imbalanced pH Levels

When pH is too high (>7.8), chlorine becomes ineffective. When too low (<7.2), it burns off too quickly. Keep pH between 7.2-7.6 for optimal chlorine performance.

How to Fix a Green Pool in 5 Steps

  1. Step 1: Test & Balance Water Chemistry
    Test pH, chlorine, and alkalinity. Adjust pH to 7.2-7.6 before shocking.
  2. Step 2: Shock the Pool
    Add 2-3 lbs of calcium hypochlorite shock per 10,000 gallons. Run pump overnight.
  3. Step 3: Brush Thoroughly
    Brush walls, floor, and steps to loosen algae. Pay special attention to corners.
  4. Step 4: Filter 24/7
    Run your filter continuously until water clears. Clean/backwash filter daily.
  5. Step 5: Vacuum to Waste
    Once clear, vacuum dead algae to waste (not filter). Repeat if needed.

Prevention: Keep Your Pool Clear

  • Test water chemistry weekly
  • Maintain 1-3 ppm chlorine at all times
  • Run pump 8-12 hours daily in summer
  • Brush pool weekly
  • Clean filter regularly
  • Consider weekly professional service

Need Professional Help?

Don't want to DIY? Project 36 Services offers green pool recovery with 24-48 hour turnaround. Family owned, 21 years experience, 1-year warranty.

Green Pool Service Call 682-399-2593