Cloudy pool water has exactly six possible causes. Work through this diagnostic in order and you'll identify the real problem in under 5 minutes — before spending a dollar on chemicals.
The 6 real causes of cloudy water
- Low free chlorine. Check FC — should be at minimum 'FC/CYA ratio.' If below, raise chlorine and give it 24 hours.
- High CYA (chlorine lock). CYA above 80 ppm makes normal FC ineffective. Test CYA; if high, partial drain.
- Poor filtration. Pressure reading low? Pump running short? Test run-time: minimum 8 hours daily in summer.
- Dead algae. Just finished a SLAM? That's dead algae. Vacuum to waste, don't let it re-dissolve.
- High pH / high LSI. Calcium precipitating out as invisible micro-particles. Check pH and LSI.
- Fine particulates from wind or rain. Pollen, dust, runoff. Usually clears in 24–48 hours of continuous filtering.
Your 5-minute diagnostic
| Test | If abnormal |
|---|---|
| Free chlorine | Below minimum → raise FC |
| pH | Above 7.8 → lower pH |
| CYA | Above 80 ppm → partial drain |
| Filter pressure | High → clean filter |
| Pump runtime | Less than 8 hrs → extend |
| Recent SLAM / event | Yes → clarifier + filter time |
Clarifiers and flocculants
Clarifier clumps fine particles so the filter can catch them. Good for persistent haze from organic matter. Adds 24–48 hours of filter runtime.
Flocculant (“floc”) drops everything to the bottom as a cloud. You turn off the pump, let it settle overnight, then vacuum to waste. Useful for post-SLAM or heavy particulate — not for routine cloudiness.
When to call a pro
Cloudy for more than 72 hours after chemistry is corrected? Filter clean, chemistry in range, and still cloudy? Something else is going on — possibly a plumbing leak re-introducing contaminants, a failed salt cell not producing, or a metal staining event. That's a visit, not a home fix.