Why is my pool green and how do I fix it?
A pool turns green when free chlorine drops to zero long enough for algae to bloom, usually after a missed week, a storm, a failed pump or stabilizer so high that the chlorine present cannot work. Recovery means circulation, correct pH, sustained shock and repeated filter cleaning — typically three to seven days.
The usual causes
- Service lapsed for two or more weeks
- Heavy rain diluted the water and dropped chlorine
- Pump or timer failed and the water stopped circulating
- Cyanuric acid climbed so high that chlorine is locked up
- Salt cell scaled over and stopped producing
- Filter is dirty enough that debris keeps recirculating
The recovery sequence
- Confirm the pump runs and circulation is real
- Remove leaves and debris so chlorine is not wasted on them
- Bring pH into range first, or shock will not work well
- Shock and hold a chlorine residual until the green is gone
- Brush every surface daily — algae hides in rough plaster
- Clean or backwash the filter repeatedly as it loads with dead algae
- Test stabilizer once clear; drain and dilute if it is too high
Water that stays cloudy grey after the green clears is dead algae the filter has not caught yet. That is progress, not failure. Water that keeps going green after treatment usually points to stabilizer, a phosphate load, or a circulation problem that has not been fixed.