A sparkling blue pool is the centerpiece of any backyard — but when the water suddenly turns green, it becomes an eyesore and a sign that something is wrong. Green pool water is one of the most common issues pool owners face, and fortunately, it can usually be fixed quickly with the right approach. This guide explains the causes of green pool water, step-by-step green pool water treatment methods, and how to keep the problem from returning.
What Causes Green Pool Water?
Green water is almost always a sign of algae growth, but multiple underlying issues can trigger it:
1. Low Chlorine Levels
Chlorine is the main sanitizer in pools. When it drops too low, algae can grow rapidly—especially in warm weather.
2. Poor Filtration
If the pool filter is clogged, dirty, or not running long enough, water becomes stagnant and algae thrive.
3. Imbalanced Water Chemistry
Improper pH, alkalinity, or cyanuric acid (CYA) levels reduce chlorine’s ability to sanitize effectively.
4. Heavy Rain or Debris
Rainwater and organic matter (leaves, dirt, pollen) introduce contaminants that feed algae.
5. Metals in the Water
Iron or copper can turn water green as they oxidize, though this is less common than algae-related issues.
Green Pool Water Treatment: Step-by-Step
Follow these steps to clear up a green pool quickly and safely.
Step 1: Test the Water
Use a reliable test kit or strips to check:
- Free chlorine
- pH
- Alkalinity
- CYA (stabilizer)
Record the results — they’ll guide your treatment plan.
Step 2: Balance the pH
Algae blooms often cause high pH, which weakens chlorine.
- Ideal pH range: 7.2–7.4
- Adjust using pH reducer (muriatic acid or sodium bisulfate) as needed.
Step 3: Brush the Pool Surfaces
Algae cling to:
- Walls
- Steps
- Floors
- Ledges
Brush thoroughly to break their grip and expose them to chlorine.
Step 4: Shock the Pool
Pool shock is a high dose of chlorine designed to kill algae quickly.
How much shock do you need?
- Light green water: 1–2 pounds per 10,000 gallons
- Dark green water: 3–4 pounds per 10,000 gallons
- Black/very dark green: 5+ pounds per 10,000 gallons
Broadcast shock evenly across the surface with the pump running.
Step 5: Run the Pump Continuously
Keep your filtration system running 24–48 hours straight after shocking.
This helps circulate chemicals and filter out dead algae.
What If the Water Is Still Green After Treatment?
If the pool remains green:
- Re-test chlorine and pH levels
- Shock the pool again
- Ensure the pump and filter are functioning properly
- Check for phosphates (they feed algae)
Persistent green water usually means the chlorine demand is still not met or filtration is insufficient.
Final Thoughts
Green pool water is a common but fixable problem. With proper water chemistry, regular filtration, and routine maintenance, you can keep your pool clear, inviting, and algae-free. By following this green pool water treatment guide, you’ll restore clarity quickly — and keep it that way all season long.
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