Green pool water: the complete solution against algae
Green water means algae have taken over, almost always from a lack of active chlorine. The method to rescue it is proven: balance the pH, shock-chlorinate, brush, and filter non-stop.
In short
Green water is an algae bloom, encouraged by insufficient or ineffective chlorine, filtration that is too short and heat. In the vast majority of cases it is treated without draining: bring the pH into the right range so chlorine works, carry out a shock treatment, brush the walls and filter continuously until the water clears.
Why water turns green
Algae develop as soon as disinfection weakens. The causes often add up: a chlorine level that is too low, a pH that is too high and makes chlorine ineffective, insufficient filtration, high heat, or an excessive stabiliser level that "locks" the chlorine despite a correct dose.
The case of locked chlorine
If you add chlorine with no visible effect, suspect a stabiliser level that is too high (above about 70 mg/L). The chlorine is then present but inactive. In that specific case, renewing part of the water is the only lasting solution, alongside the shock treatment.
Preventing a relapse
Once the water is clear, keep chlorine steady, the pH between 7.0 and 7.4 and filtration matched to the temperature. It is day-to-day balance, more than shock treatments, that stops the water from turning green again.
What to do, step by step
Set the pH first
Bring the pH to between 7.0 and 7.4. Above that, the shock treatment is largely wasted because chlorine works poorly in overly alkaline water.
Carry out a shock treatment
Apply a shock treatment to quickly break the algae bloom, with filtration running.
Brush walls and floor
Vigorously brush the walls, floor and corners: clinging algae resist treatment until they are dislodged.
Filter continuously
Let filtration run without interruption until the water clears. Clean the filter regularly, as it will load up.
Clarify and adjust
A flocculant helps capture dead algae in suspension. Then check the water balance and, if chlorine remained ineffective, check the stabiliser.
Frequently asked questions
Can green water be rescued without draining?
Yes, in the vast majority of cases: pH, shock chlorine, brushing and continuous filtration are enough. A partial drain is only needed if the stabiliser is too high and locks the chlorine.
How long to get clear water back?
Often 2 to 4 days depending on severity, provided you filter continuously and brush. Very green water may need several successive treatments.
How do I stop the water turning green again?
By keeping steady chlorine, a pH between 7.0 and 7.4 and filtration matched to the water temperature every day. Prevention is about consistency, not shock treatments.