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 reduces FC effectiveness — you need a higher FC to compensate (FC/CYA ratio). 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.
Frequently asked questions
A clarifier clumps fine particles together so your filter can catch them, adding 24 to 48 hours of filter runtime. It is good for persistent haze from organic matter. A flocculant drops everything to the bottom as a cloud instead. You turn off the pump, let it settle overnight, then vacuum to waste. Floc is for post-SLAM or heavy particulate cleanup, not routine cloudiness.
Yes. CYA above 80 ppm reduces how effective your free chlorine is, so you need a higher FC to compensate for the same result. That is chlorine lock. If your chlorine reads fine but the water stays cloudy, test CYA. If it is above 80 ppm, a partial drain to lower it is the fix rather than dumping in more chlorine.
Run the filter at least 8 hours a day in summer as a baseline. Fine particulates from pollen, dust, or storm runoff usually clear within 24 to 48 hours of continuous filtering. If you add a clarifier, plan on another 24 to 48 hours of runtime for the filter to catch the clumped particles. Short pump runtime is one of the six real causes of cloudy water.
Yes, if you just finished a SLAM, cloudy water is usually dead algae. Vacuum it to waste rather than letting it re-dissolve back into the pool. For a heavy load, a flocculant works well here: drop everything to the bottom, let it settle overnight with the pump off, then vacuum to waste. It clears faster than waiting on the filter alone.
If your filter is clean, your chemistry is in range, and the water is still cloudy more than 72 hours later, something else is going on. It could be a plumbing leak re-introducing contaminants, a failed salt cell that is not producing chlorine, or a metal staining event. At that point it is a service visit, not a home fix, because the cause is no longer in the water chemistry.
It can. When pH climbs too high and your LSI goes positive, calcium precipitates out of the water as invisible micro-particles that read as haze. Check pH and LSI. If pH is above 7.8, lower it. This is common in South Florida with hard fill water, and it is one of the six real causes, so rule it out before assuming the problem is filtration or algae.
Want a pro to handle this?
Our CPO-certified techs run this exact playbook on every weekly service visit.