Domakihub Pool Water Milky White? Fix Calcium Precipitation Fast
How to clear calcium carbonate clouding without draining your pool.
Reviewed by Domakihub pool pros · 2026-06-23 · 5 min read
That dense, milky-white haze in your pool is not the same as ordinary cloudiness — it signals a specific chemical event called calcium carbonate precipitation, where dissolved calcium solidifies and scatters light. The video above walks through the underlying chemistry in detail. This article translates that into a practical, step-by-step fix for homes, holiday rentals, and hotels across Greece, where hard water and intense summer sun make this problem especially common.
What Actually Causes the Milky-White Haze
Calcium carbonate precipitation happens when three factors stack up simultaneously: pH above 7.8, total alkalinity above roughly 120 ppm, and calcium hardness above 400 ppm. When all three climb at once, the water becomes supersaturated — it simply cannot hold that much dissolved calcium any longer, so the calcium bonds with carbonate ions and drops out of solution as fine, white particles suspended throughout the water.
Greek tap water and borehole water tend to arrive already high in calcium and bicarbonates. Add summer heat, strong UV, and the evaporation that drives up calcium concentration in a partly filled pool, and precipitation can happen overnight. It is not a hygiene failure — your sanitiser may be perfectly fine — but it will not clear on its own, and the deposited scale will coat your tiles, pump, and heat exchanger if left untreated.
Why Shocking and Backwashing Are Not Enough
Many pool owners respond to any cloudiness by adding chlorine and running the filter harder. For calcium precipitation this is largely wasted effort. The particles are not organic; extra oxidiser does not dissolve them. A filter will eventually catch some, but new particles keep forming as long as the water remains supersaturated. The root cause is a chemistry imbalance, not a sanitation shortfall.
The correct approach is to pull the Langelier Saturation Index (LSI) back into balance — a negative or near-zero LSI tells you the water will stop precipitating and begin slowly redissolving what has already formed. That means methodically lowering pH first, then alkalinity, before touching calcium hardness.
Five Steps to Clear Calcium Precipitation Without Draining
- 1
Test the full chemistry panel, not just chlorine
Before adding anything, measure pH, total alkalinity, calcium hardness, cyanuric acid, and temperature. Record all values. You need the complete picture to calculate your LSI and know exactly how far out of range you are. A basic two-in-one test strip will mislead you here — use a proper liquid test kit or take a water sample to a pool shop.
- 2
Lower pH to 7.2 with muriatic acid
Add muriatic (hydrochloric) acid in small doses, broadcast across the deep end with the pump running. Target pH 7.2, which is slightly acidic enough to begin dissolving precipitated calcium carbonate without stressing swimmers or equipment. Always add acid to water, never the reverse, and allow 30 minutes of circulation between doses. Retest before each addition.
- 3
Reduce total alkalinity to 80–100 ppm if elevated
High alkalinity acts as a pH buffer that fights your acid additions and keeps conditions favourable for more precipitation. To reduce it, add acid in a concentrated area with the pump off, let it sit for an hour, then circulate. This targeted technique preferentially drives off bicarbonates as CO2 without pulling pH as sharply. Repeat over several days rather than overcorrecting in one session.
- 4
Run your filter continuously and clean it daily
While chemistry stabilises, the filter is your mechanical ally. Run it 24 hours a day and backwash or rinse the cartridge every 24 hours. Calcium carbonate particles are very fine and will blind a cartridge filter quickly, reducing flow and effectiveness. If you have a sand filter, add a clarifier flocculant to help particles clump and settle to the floor for vacuuming to waste.
- 5
Verify the LSI is negative before returning to normal dosing
Once the water clears, recheck all parameters and calculate the LSI (many pool-app calculators do this instantly from your test readings). An LSI between −0.3 and 0 confirms the water is mildly aggressive enough to dissolve residual scale without damaging plaster or grout. Only then resume normal maintenance schedules. In future, check the LSI at the start of every season and after any significant rainfall or refill.
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FAQ
- Can I just partially drain and refill to fix milky-white water?
- Partial draining can help when calcium hardness is very high — above 600 ppm — because dilution is the only way to lower calcium hardness itself. However, if pH and alkalinity are the primary drivers and calcium hardness is only moderately elevated, a chemical correction is faster, cheaper, and avoids the water waste. In most Greek cases the chemistry fix alone is sufficient.
- How long does it take for the water to clear once chemistry is corrected?
- With continuous filtration and correct chemistry, mild precipitation typically clears within 48 to 72 hours. Heavy precipitation can take four to seven days. Running the pump around the clock and cleaning the filter daily makes a significant difference. Do not add a flocculant and then run the pump — floc needs 8 hours of still water to settle particles to the floor before you vacuum them out.
- Will this happen again next summer?
- It will if your fill water is naturally hard. The practical prevention is to check your LSI at pool opening each season, after significant top-ups, and after heavy rain (which raises alkalinity as it washes dust into the water). Keep pH between 7.4 and 7.6 and alkalinity between 80 and 110 ppm, and consider a sequestering agent at the start of summer to keep calcium in solution during the hottest months.