Why is my pool cloudy?
Cloudy water is a symptom, and the appearance narrows the cause faster than any test does. Milky white, green-tinted, dull grey and hazy-after-a-storm are four different problems. Start by matching what you see.
Match what you see to what it probably is
| What it looks like | Most likely cause | First move |
|---|---|---|
| Milky white, no green | High pH with high calcium hardness, or fine dead-algae particles | Test pH and calcium before adding anything |
| Green tint or a green cast in the deep end | Algae starting — sanitiser is not keeping up | Check free chlorine against your CYA level |
| Dull grey haze, no colour | Filtration or circulation — flow, runtime or a loaded filter | Read the pressure gauge against its clean baseline |
| Cloudy after a storm or heavy rain | Suspended debris and silt the filter cannot catch quickly | Clean the filter, then let it run |
| Cloudy right after adding chemicals | Precipitated particles or dead algae — often temporary | Run the filter and re-test before adding more |
The 30-second triage
- Look at the pressure gauge. Above its clean baseline by 8–10 psi means the filter is the bottleneck.
- Look at the returns. Weak or bubbly flow means a suction problem or air in the system.
- Test pH, free chlorine and cyanuric acid. Those three explain most chemistry-side cloudiness.
- Ask when it started. Cloudiness that appeared overnight after rain is not the same as one that crept up over a week.
For the full ordered method, read cloudy pool water: what to check, in order. This page is the shortcut; that one is the procedure.
Why filtration is the first suspect
Most cloudy pools are under-filtered, not under-dosed. The filter removes particles; chemicals change what is dissolved. If the filter is loaded, channelling or simply not running long enough, no amount of clarifier will fix the cause.
- Check the pressure gauge and clean the filter when it is up 8–10 psi — see how to backwash a pool filter.
- Check runtime. A pump that runs too few hours never completes a turnover — calculate your turnover time.
- Check the baskets and the impeller. A restricted pump delivers weak flow without the gauge telling you.
- Check circulation. Misdirected returns leave dead spots that never clear.
When the cause is chemistry
- High pH with high calcium hardness. Calcium comes out of solution and hangs as a milky haze — common after topping up with hard fill water.
- High cyanuric acid. Stabiliser above range means your free chlorine reading is doing less work than it looks like, and algae gets a foothold. Check it with the CYA calculator.
- Dead algae. Once an algae bloom is killed, the carcasses are fine particles that a sand filter struggles to catch. This is the one case where a clarifier genuinely helps.
- Low total alkalinity. pH becomes unstable and swings, which drags other readings around with it.
What not to do
- Do not add clarifier before checking the filter. You will mask the symptom and keep paying for chemicals.
- Do not change pH, alkalinity and chlorine all at once. One change, then retest.
- Do not keep adding sanitiser when the reading already looks fine — check CYA first.
- Never mix chemicals, and always add chemicals to water rather than water to chemicals.
Cloudy water questions
Is cloudy pool water safe to swim in?
Treat it as not safe until you know the cause. Cloudy water can hide a swimmer in trouble, and if the cause is algae or low sanitiser, the water quality is the issue rather than the clarity.
Will cloudy water clear on its own?
Sometimes, if it was stirred-up debris and the filter is working — it may clear in a day or two of running. If it has not improved in 48 hours, the cause is something that needs fixing.
Does shock clear a cloudy pool?
Only if the cause is something shock addresses. If the filter is loaded or circulation is poor, shocking adds load to a filter that is already the bottleneck.
Why is only the deep end cloudy?
Poor circulation and stratification. The deep end turns over slowly, so debris and fine particles accumulate there. It is a circulation problem as much as a filtration one.
Related
- Cloudy pool water — what to check, in order
- How to backwash a pool filter
- How long to run a pool pump
- Pool filter fix — troubleshooting by symptom
- CYA / stabiliser calculator
Review status: Water clarity and algae. Last reviewed 2026-09-13. See the source and review status of every formula →