What Causes Swimming Pool Water to Turn Green?

Green swimming pool water is one of the most common issues faced by pool owners. The main cause is algae growth, which occurs when disinfection is insufficient. High levels of nutrients such as nitrogen and phosphorus accelerate algae reproduction, and warm water temperatures provide an ideal environment. During hot seasons, algae can multiply rapidly, turning a clean pool green in just a few days.

What Is Algae?

Algae are microscopic organisms that grow in water. Most algae are plant-like, but there are exceptions:

Blue-green algae: Actually cyanobacteria, capable of forming harmful blooms.

Pink algae: More closely related to fungi than plants.

When conditions are favorable, algae blooms not only turn pool water green but also:

Reduce water clarity

Provide breeding grounds for bacteria

Pose potential health risks for swimmers

How to Fix Green Pool Water

If your pool water has already turned green, follow these steps:

Shock the Pool with Chlorine

Raise chlorine levels to destroy algae quickly.

Use an Algaecide

Common options include quaternary ammonium salts and copper-based algaecides, which help chlorine eliminate algae more effectively.

Remove Excess Nutrients

Algae feed on nitrogen and phosphorus. Use a phosphate remover to limit their growth.

Clean the Pool Thoroughly

Brush walls and floors to remove dead algae

Vacuum debris

Backwash the sand filter to maintain circulation

Balance the Water Chemistry

Maintain proper pH (7.2–7.8) and chlorine levels (1–3 ppm).

How to Prevent Pool Water from Turning Green

Prevention is easier than treatment. Regular maintenance will help you keep pool water crystal clear:

• Test water regularly for pH, chlorine, and turbidity
• Maintain chlorine at safe levels to stop algae growth
• Control nutrients, especially phosphorus
• Clean or replace filters to ensure proper circulation
• Brush and vacuum the pool weekly
• Schedule regular water replacement if necessary

By following these practices, you can significantly reduce the risk of green pool water.

Safety Reminder

When using chemicals such as chlorine or algaecides, always follow expert advice and the instructions on product labels. Proper handling ensures both effective disinfection and swimmer safety.

Yuncang Chemical offers a wide range of pool treatment solutions, including chlorine products, algaecides, and phosphate removers. Visit our official website to learn more.