Answer three quick questions about your pool and get the most likely cause of the cloudiness, with the fix spelled out step by step.
Most likely cause
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Rule-of-thumb triage, not a lab test. If water is green-tinged, treat it as algae — see the green pool calculator.
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The three causes of cloudy water
Nearly every cloudy pool is one of three things. Chemistry: chlorine too low, letting micro-organisms bloom just enough to haze the water (the fix is chlorine). Filtration: the filter isn't running enough hours or is dirty, so fine particles never get removed (the fix is run time and a cleaning). Debris load: something dumped particles in all at once — dead algae after a kill, sunscreen and skin from a pool party, dust from a storm (the fix is patience, 24/7 filtering, and maybe a clarifier).
The overnight test that sorts chemistry from filtration
Test free chlorine at dusk and again before sun hits the pool. Losing more than 1 ppm overnight means something alive is eating chlorine — treat it as early algae. Holding steady overnight means the chlorine side is fine and the cloudiness is mechanical: filter longer, clean the media, add clarifier if needed.
When cloudy is a warning, not a nuisance
Cloudy water with low chlorine is how green pools start — you're often 24–48 hours from visible algae. That combination deserves same-day action: dose to target with thechlorine calculator, run the pump continuously, and retest in the morning.
Frequently asked questions
Why is my pool cloudy but chlorine is fine?
Then it's usually mechanical, not chemical: the filter isn't running long enough (under 8 hours a day while fighting cloudiness), the filter media is dirty or worn, or fine particles are too small for the filter to grab. More run time and a filter clean solve most of these.
Will shock clear a cloudy pool?
Only if the cloudiness is biological — early algae or contamination after heavy use. If free chlorine is already at target and holding overnight, more chlorine won't clear water that just needs filtering.
Should I use a clarifier or flocculant?
Clarifier clumps fine particles so your filter can catch them: gentle, slow, safe. Flocculant sinks everything to the floor for a manual vacuum to waste: fast but laborious and it wastes water. Try run time + clarifier first; save floc for swamp recoveries.
How long does it take for a cloudy pool to clear?
With the cause fixed and the pump running 24/7: light haze often clears in 24–48 hours; milk-white water after an algae kill can take 3–7 days of continuous filtering with filter cleanings whenever pressure rises.