How to clear cloudy pool water
Updated:
Cloudy water usually comes from one of three things: not enough chlorine, high pH or alkalinity, or a filter that needs help. Balance the water, make sure sanitizer is adequate, and give the filter time.
What clouds pool water
The MAHC Annex names the usual causes. High alkalinity pushes pH up, and high pH brings cloudy water, scale and weaker chlorine. Too much calcium causes cloudiness and scale. A saturation index (LSI) above +0.3 can cause scale, cloudy water and filter problems, and dissolved solids that keep climbing can cause staining and cloudy water too. Low chlorine is the other common cause, and Trouble Free Pool treats a cloudy pool with the same full shock it uses on a green one.
Readings to check
| Reading | Aim for | Source |
|---|---|---|
| Free chlorine | At least the minimum for your CYA (7.5% of CYA) | TFP chart; CDC floor of 1 ppm, or 2 ppm with CYA |
| Combined chlorine | 0.5 ppm or less | TFP; the MAHC action level for public pools is 0.4 (5.7.4.4.2) |
| pH | 7.2–7.8; 7.2–7.6 when balancing | Hayward and Pentair manuals; MAHC Annex 5.7.4.6. The CDC allows 7.0–7.8 |
| Total alkalinity | 80–120 ppm | Hayward and Pentair manuals; the MAHC allows 60–180 |
| Calcium hardness | 200–400 ppm; 80–200 for vinyl or fiberglass | MAHC Annex 5.7.4.4.3 and 5.7.4.6 |
| Water balance (LSI) | −0.3 to +0.3 | MAHC Annex 5.7.4.6 |
Step by step
- Check sanitizer firstTest free and combined chlorine. If free chlorine is below the minimum for your CYA, or combined chlorine is above 0.5 ppm, the level at which Trouble Free Pool says to look closer, raise chlorine first. Public pools must act at 0.4 ppm under the MAHC. Hazy water that keeps using chlorine up gets the same full shock as a green pool.
- Balance pH and alkalinityBring pH into 7.2–7.6 and alkalinity into 80–120 ppm, the Hayward and Pentair range. High alkalinity keeps pushing pH up, and the MAHC Annex links high pH to cloudy water, scale and weaker chlorine.
- Run the filter longerRun the pump around the clock until the water clears. Clean or backwash when the pressure gauge reads 25% above its clean reading, the point Trouble Free Pool uses.
- Check calcium and dissolved solidsIf chlorine and pH are right and the haze stays, test calcium hardness and total dissolved solids. The MAHC Annex ties high calcium, and dissolved solids well above the 1,500 ppm over fill water it treats as generally accepted, to cloudy water. Both come down only by replacing water.
- Add a clarifier if neededIf balanced and still hazy, a clarifier clumps fine particles so the filter can catch them. Flocculant is different: it drops everything to the floor to be vacuumed to waste, never through the filter. Use either exactly as its label directs, which the MAHC requires of public pools (5.7.3.3.2).
FAQ
Why is my pool cloudy after shocking?
Usually dead algae still in suspension, and sometimes high pH. Keep the pump running, brush, and clean the filter when its pressure climbs. If you shocked for algae, keep going until the overnight loss is 1 ppm or less, since lingering haze can mean the job is unfinished.
Is cloudy water safe to swim in?
Not if you cannot see the bottom. The MAHC requires the bottom of a public pool to be visible whenever it is open (5.7.6.1), and cloudy water often signals a sanitizer or balance problem as well.
Sources
- CDC, Model Aquatic Health Code, 5th edition (2024), Code Language. Sections 5.7.3.3.2 (clarifiers and flocculants), 5.7.4.4.1 (alkalinity), 5.7.4.4.2 (combined chlorine) and 5.7.6.1 (bottom visible)
- CDC, Model Aquatic Health Code, 5th edition (2024), Annex. Sections 5.7.4.4.1 (alkalinity and pH), 5.7.4.4.3 (calcium) and 5.7.4.6 (LSI and dissolved solids)
- CDC, Home Pool and Hot Tub Water Treatment and Testing (May 10, 2024). Free chlorine minimums and the pH range
- Trouble Free Pool, CYA Chlorine Relationship (Chlorine/CYA chart). Minimum free chlorine as 7.5% of CYA
- Trouble Free Pool, SLAM Process Checklist (V2). Filter cleaning at 25% above clean pressure
- Trouble Free Pool, Perform the Overnight FC Loss Test (OCLT). The overnight chlorine loss test
- Trouble Free Pool, Pool Chemistry ABC’s. Combined chlorine above 0.5 ppm calls for a closer look
- Hayward, AquaRite 900 Series Electronic Chlorine Generator manual (092623 Rev D). pH 7.2–7.8 and total alkalinity 80–120 ppm
- Pentair, IntelliChlor IC15/IC20/IC40/IC60 Installation and User’s Guide (P/N 520589 Rev. R, 2023). pH 7.2–7.8 and total alkalinity 80–120 ppm
Related
Stop guessing. Get the exact fix
DoseMyPool turns your test numbers into the precise doses and the safe order to add them. Free on the App Store.