Symptoms
- Water has a green or greenish tint
- Slippery or slimy feel on pool walls and steps
- Visible green patches on surfaces below the waterline
Likely causes
- CommonLow or depleted chlorine allowing algae to bloomAlgae spores are always present and multiply quickly once sanitizer drops too low.
- CommonPoor water circulation or a broken pump/filterStagnant areas of the pool are more prone to algae growth.
- PossibleHigh phosphate levels from fertilizer runoff or debrisPhosphates act as an algae food source.
- PossibleHeavy rain diluting chemical levelsRainwater can dilute chlorine and introduce organic debris that feeds algae.
What to do
- Test and record chlorine, pH, and alkalinity levels before treating.
- Brush all pool walls, steps, and corners vigorously to break up algae before shocking.
- Add a heavy dose of pool shock (often double or triple the normal dose for green water) following product instructions.
- Run the filter continuously around the clock until the water clears from green to cloudy to clear.
- Vacuum the pool floor once algae has settled, using a 'waste' or 'backwash' filter setting if available to avoid recirculating debris.
- Retest and rebalance chemicals once clear, and consider an algaecide for ongoing prevention.
Tools and parts
- Pool brush
- Pool vacuum
- Pool test kit
Pool shock treatmentSearch: “pool shock chlorine treatment”
AlgaecideSearch: “pool algaecide treatment”
When to call a pro
For a severe or recurring algae bloom, or if you suspect equipment isn't circulating water properly, a pool professional can diagnose the root cause.
Safety
Use caution
Keep swimmers out of the pool during heavy shock treatment and until chlorine returns to a safe swimming range.