Green water needs both a sanitation assessment and a filtration check. Color alone does not identify the cause, and a universal double-shock recipe is not a diagnosis.
Keep the pool closed while conditions are uncertain
Do not swim when water obscures the bottom or when sanitation has not been verified. A clear-looking pool is not proof of safe water either. Collect an overview photo and note when the change began, recent treatments, rain, debris and refill history.
Gather evidence before choosing treatment
- Test free and combined chlorine, pH and CYA with a kit whose range covers the current condition; obtain calcium and alkalinity readings as well. Record gallons and all recent product additions.
- Check whether the pool has actual circulation, normal water level, visible return flow and a functioning sanitizer. Record pump speed and filter pressure against the clean baseline at the same speed.
- Describe whether green material brushes off the walls, whether the water is clear green or opaque, and whether staining followed a chemical addition. These observations help distinguish possible algae from other causes; they do not confirm a diagnosis.
Treatment and progress checks
Choose the sanitizer label and an equipment-compatible plan from the measured results. Skim debris and use a brush approved for the finish. Monitor filter loading and treatment progress instead of prescribing a fixed 24-hour run or repeated escalating doses. Do not add flocculant unless the product and filter support the required removal method.
Send useful information to CAS
Provide test results, equipment models, current and clean filter pressures, photographs and the products already used. This makes a repair or cleanup request more actionable and helps avoid buying incompatible chemicals.
Sources and scope
Documentation checked October 11, 2026. Manufacturer examples apply only to the named equipment; confirm your model and revision. This is homeowner assessment and planning guidance, not a claim that your equipment has been inspected.
- CDC: Keeping your pool safe and healthy — Drowning prevention and chemical handling
- CDC: Use pool chemicals safely — Product labels, PPE, incompatible chemicals and pre-dissolving
- Pentair: Filter product safety help center — Manufacturer recommends professional filter maintenance
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