Cloudy pool water: the 3 causes and how to clear it
- Three families of causes: insufficient filtration, unbalanced chemistry (pH, sanitiser), micro-particles or early algae.
- A water test separates the suspects in 30 seconds.
- Extended filtration + chemical correction solve most cases; flocculant/clarifier for fine particles.
- Cloudy water turning pale green = algae getting started: act fast.
Cloudy pool water has three families of causes: insufficient filtration (run time too short or a clogged filter), unbalanced chemistry (pH too high, sanitiser too low), or particles too fine for the filter — including early-stage algae. To tell them apart: test the water, check the filter, and look at the colour of the haze. The treatment combines chemical correction, extended filtration and, if needed, a flocculant or clarifier. The exact dose and order depend on your pool: the CliniPool app sorts it out for you.
First, identify the suspect
The haze is uniform and the water looks “tired”? Start with the filtration: a daily run time too short for the water temperature is the number one cause, especially in summer. Check the filter pressure and the pump basket too.
The water leans pale green, the walls feel a little slippery? That’s algae getting started. You’re 24-48 hours away from properly green water: treat now, it’s ten times easier.
The water is whitish, milky? That’s more a pH/alkalinity/limescale imbalance — a case of its own, covered in the milky water guide (“Also worth reading”).
Just finished a shock treatment? The cloudiness is often the logical sequel: the destroyed organisms turn the water whitish, and filtration removes them in a day or two.
In every case, the starting reflex is the same: a full water test. Without numbers, you guess; with them, you know.
The clearing plan
1. Test the water — pH, sanitiser, alkalinity, stabiliser. The app’s strip photo does it in 30 seconds.
2. Correct the chemistry. A high pH is cloudy water’s classic accomplice: it weakens the chlorine AND encourages limescale deposits. Corrector amounts depend on your volume and your gap — that’s the app’s job.
3. Filter long. Continuously until the water is clear. Clean the filter when the pressure climbs, not out of habit: every clean also drains away treated water.
4. Help the filter if necessary. If the water stays hazy after 48 h of filtration with correct chemistry, the particles are too fine: flocculant (sand filter) or clarifier (cartridge) depending on your setup. The app tells you which one is compatible with YOUR filter — get it wrong and you clog a cartridge.
5. Re-test. Clear water doesn’t mean balanced water: one last test confirms everything is back in order.
If that’s not enough
Cloudiness that survives all of the above usually hides either a filter at the end of its life (sand to replace, worn cartridge), a stabiliser too high leaving the sanitisation flat despite decent-looking numbers, or phosphates feeding a persistent micro-algae. The app’s full test points to the right scenario instead of piling on products at random.
Frequently asked questions
Why is my water cloudy after a shock treatment?
It's often a good sign: the shock killed algae and micro-organisms, whose remains turn the water whitish. Continuous filtration captures them in 24-48 h. A clarifier can speed things up.
How long should I filter to clear cloudy water?
Continuously until it clears, then back to the normal rhythm set by the water temperature. The app calculates the right filtration time for your pool, weather included.
Flocculant or clarifier — what's the difference?
Both clump fine particles together. Flocculant (sand filters) forms clumps that sink to the floor, to be vacuumed. Clarifier (cartridge-safe) forms smaller clumps captured by the filter.
Can you swim in cloudy water?
Best avoided: if you can't see the floor, it's a safety risk (watching swimmers), and cloudiness often goes hand in hand with weakened sanitisation.