One of the most common and frustrating issues pool owners face is green pool water. It not only looks uninviting but also signals that your pool’s water chemistry is unbalanced — and potentially unsafe. Understanding why it happens and how to fix it quickly is key to maintaining a clean and safe swimming environment.
Why Does Pool Water Turn Green?
1. Algae Growth
The most common reason is algae, a plant-like organism that thrives in warm, untreated water. When chlorine levels drop, algae quickly multiplies and turns the water green — from light green to a murky swamp-like color.
2. Low Chlorine Levels
Chlorine is your pool’s main defense against bacteria and algae. If the chlorine drops too low (due to heavy use, sunlight, or poor maintenance), algae can start to grow rapidly.
3. Imbalanced pH and Alkalinity
Improper pH or total alkalinity can make chlorine less effective, leading to algae-friendly water conditions.
4. Poor Filtration or Circulation
A weak pump or clogged filter will reduce water circulation and filtration, allowing debris and contaminants to build up — perfect for algae growth.
5. Debris Accumulation
Leaves, dirt, and organic matter left in the pool decompose and can introduce nutrients that feed algae.
How to Fix Green Pool Water
Step 1: Test the Water
Use a pool test kit or strips to check chlorine, pH, and alkalinity levels. This helps you know exactly what needs to be adjusted.
Step 2: Shock the Pool
“Shocking” the pool means adding a large dose of chlorine or a specialized shock treatment to kill algae. You may need to double or triple shock depending on how green the water is:
- Light green: 1x shock
- Dark green: 2x shock
- Swamp green: 3x shock
Tip: Do this in the evening so the sun doesn’t burn off the chlorine too quickly.
Step 3: Brush & Vacuum the Pool
Use a pool brush to scrub the walls, steps, and floor — especially in corners where algae hides. Then vacuum the debris to waste or use a robotic cleaner.
Step 4: Run the Filter Continuously
Keep your pool pump and filter running 24/7 for at least 2–3 days until the water clears. Backwash or clean the filter as needed to maintain efficiency
Step 5: Re-test and Balance Chemicals
Once the algae is gone and the water clears up, recheck the water chemistry and balance pH (7.4–7.6), alkalinity (80–120 ppm), and chlorine (1–3 ppm).
What NOT to Do
- Don’t swim while the water is green or being treated.
- Don’t skip brushing — chlorine can’t kill algae clinging to surfaces.
- Don’t forget to clean the filter after killing algae — dead algae can clog it fast.
How to Prevent Green Pool Water
- Test water at least 2–3 times a week
- Maintain proper chlorine and pH levels
- Run your pump daily (8–12 hours in summer)
- Skim and vacuum regularly Shock the pool weekly or after heavy use/rain
- Use algaecide as a preventative (optional)
Conclusion:
Green pool water is a sign your pool needs urgent care, but it’s 100% fixable with the right approach. Acting quickly, using proper chemicals, and maintaining a regular cleaning routine will bring back your clear blue water in no time — and keep it that way.
