A green pool is not just an eyesore — it is a health hazard. Green algae is almost always accompanied by harmful bacteria, increasing the risk of skin rashes and eye and ear infections. The good news is that no matter how bad it gets, there is always a way to fix it.
Why is My Pool Green?
In almost every case, a green pool means you have an active algae bloom. Green algae thrive when pool conditions allow them to — and several factors usually combine at once:
Low free chlorine
The primary cause — algae cannot establish when chlorine levels are adequate
High temperatures
Warm water accelerates algae growth and depletes chlorine faster through evaporation
Heavy rain
Dilutes chlorine and salts while adding nitrates and phosphates that feed algae
High pH
pH above 7.6 drastically reduces chlorine effectiveness, leaving the pool vulnerable
High humidity
Creates ideal environmental conditions for rapid algae growth
High phosphate levels
Phosphates act as a food source for algae, accelerating bloom development
What About Copper Ionized Pools?
In pools sanitised by copper ionizer, a green colour can occasionally indicate excess copper rather than algae. If copper levels exceed 0.6ppm, or too much oxidizer is added, copper turns into copper oxide — a bright green colour that tints the water. The only fix is to reduce the copper level and allow the pool time to revert naturally.
How to Prevent a Green Pool
Prevention is far less work than treatment. A few consistent habits are all it takes:
Maintain free chlorine at around 3ppm through summer
This alone will prevent algae growth even under otherwise ideal conditions.
Keep pH below 7.6
High pH dramatically reduces chlorine effectiveness. Check and balance pH regularly.
Shock weekly
Weekly shock treatment reduces cloudy water and stops early-stage algae growth before it takes hold. Always add algaecide after shocking, never at the same time.
Use algaecide regularly
A regular algaecide dose keeps algae suppressed between shock treatments.
Brush walls, floor and steps regularly
Use an algae brush for a thorough clean. Avoid wire brushes on fibreglass, vinyl, acrylic and painted surfaces.
Keep filters, skimmer and pump clear
A blocked filter cannot sanitise effectively. Clean and backwash regularly.
How to Fix a Green Pool
Treatment depends on how severe the algae bloom has become. There are three broad categories:
FAQs
How long does it take a green pool to clear after shocking?
Anywhere from a few hours to a few days, depending on how severe the algae bloom is. A lightly green pool treated promptly can clear within 24 hours. A fully green or swamp-like pool will take longer.
Does rain cause green algae in pools?
Yes. Rain washes debris and organic matter into the pool, dilutes chlorine and salts, and adds nitrates and phosphates that feed algae. After heavy rain, test your water and adjust chlorine levels promptly. Remove any debris that has washed in and consider a shock treatment during extended rainy periods.
How do I remove algae from pool walls?
Brush the algae off the walls first, then apply the appropriate algaecide. Keep the circulation running for 24 hours before vacuuming or backwashing.
Is it safe to swim in a green pool?
It is not recommended. Algae depletes chlorine and creates conditions where harmful bacteria can thrive, increasing the risk of skin rashes and eye and ear infections. Treat the pool and have the water tested before swimming again.
