Cloudy water is one of the most common pool problems, and one of the most confusing, because very different causes look exactly the same. The trick is not to throw clarifier at it straight away, but to test first and work through the causes in order. Most cloudy pools fall into one of three groups: a sanitizer problem, a water balance problem or a filtration problem.
Step 1: Test before you add anything
Test free chlorine (FC), combined chlorine (CC), pH, total alkalinity, calcium hardness and stabilizer (CYA). A drop-based test kit is far more reliable than strips for this. Write the numbers down, then compare them with the table below.
| Reading | Points to |
|---|---|
| Free chlorine below the minimum for your CYA | Early algae or bacteria bloom (sanitizer problem) |
| Combined chlorine above 0.5 ppm | Chloramines and organic waste (sanitizer problem) |
| pH above 7.8, high alkalinity or high calcium | Calcium coming out of the water as fine scale (balance problem) |
| All numbers normal | Filter or circulation problem, or fine debris such as pollen |
Cause 1: Not enough chlorine
This is the most common cause. A haze that appears after hot days, heavy use or a storm is usually the very beginning of algae, before the water turns visibly green. The fix is the same as for a green pool, only shorter: raise free chlorine to shock level (about 40% of your CYA) and hold it there until the water is clear and you lose less than 1 ppm overnight. The shock calculator gives you the exact dose.
Remember that stabilizer weakens chlorine. A pool with 80 ppm CYA and 3 ppm FC is effectively under-chlorinated, even though 3 ppm "looks" fine on the test. The chlorine calculator shows the minimum level for your CYA.
Cause 2: High pH, alkalinity or calcium
When pH, alkalinity and calcium are all on the high side, the water cannot hold all its calcium in solution. Tiny particles of calcium carbonate form and the water turns milky, often right after adding cal-hypo shock or plaster work. Typical signs are a white, slightly rough film on tiles and a cloudy look that does not improve with chlorine.
- Lower pH to about 7.2–7.4 with acid. The pH calculator works out the dose.
- If total alkalinity is above 120 ppm, bring it down toward 80 ppm using the alkalinity calculator.
- If calcium hardness is far above 400 ppm, the only fix is to replace part of the water. See the calcium hardness calculator.
- Switch from cal-hypo to liquid chlorine for a while, so you stop adding calcium.
Cause 3: The filter is not keeping up
If your chemistry is fine, look at the equipment:
- Run time: run the pump long enough to turn over the whole pool at least once a day. When the water is cloudy, run it 24 hours a day until it clears.
- Dirty filter: clean or backwash when the pressure gauge reads 8–10 psi above its clean reading.
- Sand filters struggle with very fine particles. Sand older than 5–7 years may need replacing.
- Cartridge filters lose efficiency when torn or clogged with oils. Soak them in a filter cleaner a few times a season.
- DE filters leaking DE back into the pool usually have a torn grid.
- Circulation: point the return jets slightly down and in a circular pattern so there are no dead zones.
Clarifier or flocculant?
Both help with the last, stubborn haze, but only after chlorine and balance are right. They do not fix the cause.
- Clarifier clumps tiny particles together so the filter can catch them. Easy to use, works over one or two days, with the pump running.
- Flocculant (floc) drops everything to the floor overnight with the pump off. You then vacuum it to waste, which also removes water. It is faster but more work, and it does not suit cartridge filters without a waste line.
How long does it take to clear?
Once the cause is fixed, a mildly cloudy pool usually clears in 24–72 hours of continuous filtering. Heavy cloudiness after an algae bloom can take several days, because the filter has to remove all the dead algae. If the water is still cloudy after a week with good chemistry and clean filter, the filter itself is the most likely problem.
Keeping the water clear
- Keep free chlorine above the minimum for your CYA every day.
- Keep pH between 7.2 and 7.8 and alkalinity between 60 and 120 ppm.
- Clean the filter on schedule and run the pump long enough.
- Test more often in hot weather, after storms and after pool parties.
Safety first: Always read the product label. Add chemicals to water, never water to chemicals. Add one chemical at a time with the pump running, never mix products (especially chlorine and acid), and keep everyone out of the water until levels are back in range. Wear gloves and eye protection when handling acid or shock.
Sources and methodology
Last reviewed: November 2026. Doses are calculated from the chemistry of each product (molecular weights and available chlorine) and cross-checked against manufacturer and industry dosing charts. Recommended ranges follow CDC guidance for home pools and hot tubs.
Frequently asked questions
Why is my pool cloudy after shocking?
Usually for one of two reasons: the shock killed algae or organic matter and the filter still has to remove it (keep the pump running and it clears in a day or two), or cal-hypo shock added calcium to water with high pH, which forms fine scale. Lower the pH and switch to liquid chlorine if it happens often.
Can I swim in a cloudy pool?
It is not recommended. Cloudy water can hide an under-sanitized pool, and if you cannot see the bottom, you cannot see a swimmer in trouble. Wait until you can clearly see the main drain.
Will baking soda clear a cloudy pool?
No. Baking soda raises total alkalinity. If anything, high alkalinity and pH can make cloudiness worse. Fix chlorine and filtration first.