Green water looks alarming but follows a reliable recovery path: balance pH, shock hard, brush, and filter without stopping. Patience with the filter is what finishes the job.
What you are seeing
The water has a green tint that ranges from a faint cast to deep swamp green. Walls may feel slick, and the floor can look dusty where algae has settled.
Possible causes
- Low or no chlorine Algae blooms fast once sanitizer drops, especially in warm, sunny weather.
- High pH As pH climbs, chlorine loses much of its killing power even when the number looks fine.
- Poor filtration or circulation Dead spots and weak flow give algae a place to establish.
- After a storm or heavy rain Runoff adds nutrients and dilutes sanitizer, a common trigger for a bloom.
How to check
- Test chlorine and pH. Green almost always pairs with low free chlorine.
- Check whether walls feel slippery, a sign of early algae.
- Confirm the filter is clean and flow is strong before you shock.
How to fix it
- Balance pH first Lower pH toward 7.2 to 7.4 so the chlorine you add can actually work.
- Shock the pool Add a strong dose of chlorine, ideally in the evening, and run the pump continuously.
- Brush and filter Brush walls and floor to break up algae, then let the filter run around the clock, cleaning it as pressure rises.
- Repeat if needed A heavy bloom can take a few rounds of shock and brushing before the water turns cloudy white and then clears.
How to prevent it
- Hold a steady chlorine residual, never letting it hit zero.
- Keep pH in range so sanitizer stays effective.
- Brush weekly and keep circulation strong.
- Shock after storms and heavy use.