Green water means algae. It grows when free chlorine falls too low for your stabilizer (CYA) level, often after a hot week, a heavy rain, a party or a few days without testing. The fix is the same every time: the SLAM method.
What to do
- Scoop out leaves and debris so chlorine isn’t wasted on them.
- Test CYA to find your shock level, then start the SLAM method.
- Brush every surface at least once a day. Algae hides in corners, on steps and behind lights.
- Expect the water to go from green to cloudy blue to clear. The filter does the last part, so clean it often.
What to skip
Copper-based algaecides can stain surfaces and turn blond hair green, and they don’t fix the cause. “Shock” bags of cal-hypo or dichlor add calcium or more stabilizer with every dose, which makes the next green pool more likely. Liquid chlorine is enough.
Keep it from coming back
Most green pools start with free chlorine below the minimum for the pool’s CYA. Testing two or three times a week in summer and keeping FC in your target range prevents almost all of them. See the chlorine and CYA chart.