Milky or white pool water: where it comes from and how to clarify it
Whitish water — shiny but veiled — is usually not about algae but about scale: fine particles stay in suspension, often from a pH or alkalinity that is too high, or from very hard water.
In short
Unlike green water (algae) or cloudy water (filtration/pH), milky water is typically scale-related: dissolved scale precipitates into microparticles. Common causes are a high pH, high alkalinity, or very hard top-up water. You treat it by correcting the balance, sequestering the scale and filtering at length, with a flocculant as backup if needed.
Recognising scaly water
Milky water stays shiny but loses its transparency, as if veiled with white. It often appears after high heat, a poorly controlled pH correction, or in hard-water regions. A pH above 7.6 clearly speeds up the phenomenon.
Restoring the balance
The first action is to bring the pH into the right range (7.0 to 7.4): that alone often stops the precipitation. A sequestrant (anti-scale) then keeps the scale in solution, and filtration removes the particles already formed. A flocculant can clump the finest ones so the filter can capture them.
What to do, step by step
Test the pH, alkalinity and hardness
A pH or alkalinity that is too high, or very hard water, are the usual suspects.
Bring the pH to 7.0–7.4
Correct the pH first: it is often what triggers or sustains scale precipitation.
Add a scale sequestrant
An anti-scale product (sequestrant) stops scale from precipitating and helps re-clarify the water.
Filter at length, flocculate if needed
Run filtration continuously; a flocculant clumps the fine particles so the filter can retain them.
Frequently asked questions
Milky water or cloudy water — what is the difference?
Milky water stays shiny but whitish: usually scale. Cloudy water is duller and points more to insufficient filtration, an unbalanced pH or the start of algae.
Is scale dangerous?
Not for swimming, but it scales the liner, the pipes and above all the chlorinator or heat-pump exchanger, shortening their life.
Should I drain water that is too hard?
Rarely in full. Correcting the pH, sequestering the scale and filtering is usually enough. A partial renewal can help if the top-up water is itself very hard.