Fixing cloudy, milky, green or foaming water
The cause and solution for each symptom: milky, green, brown, foaming or smelly water. The fixed order of water balance, disinfection and filtration.
- cloudy water
- foam
- algae
- filtration
- troubleshooting
Short answer: cloudy water is almost always caused by one of three things: the water balance, disinfection or filtration. Always work through them in that order: first measure the pH and bring it to 7.2-7.6, then bring disinfection up to level, then clean the filter and run it continuously for 24 to 48 hours. If the water remains cloudy after that, or foams as soon as the pump starts, the water is saturated and changing it is the fastest and cheapest solution.
The fixed order
- Measure the pH (and the alkalinity). No product works with an incorrect pH; see setting the water balance.
- Bring disinfection up to level: an AquaFinesse tablet in the dispenser and the weekly liquid, or 1 to 3 ppm free chlorine if using chlorine.
- Clean the filter and let the pump run continuously for 24 to 48 hours; see backwashing the sand filter.
- Wait and measure again. Only if this does not work do you look at special causes or change the water.
By symptom
| Symptom | Most likely cause | Solution |
|---|---|---|
| Milky white | pH too high, overdose, dirty filter, or biofilm coming loose in the first weeks of AquaFinesse | bring pH to 7.2-7.6; clean the filter; filter for 24 hours |
| Greenish | algae from too little disinfection | restore pH; bring disinfection up to level (chlorine: shock); run the pump continuously; rinse the filter thoroughly; if it persists: change the water |
| Brown or rust-coloured | iron or manganese in the fill water, or corrosion | use a pre-filter when filling; if discolouration recurs, have the heater and connections checked |
| Foam | skin oils, soap and cosmetics, saturated water | shower before bathing; restore pH; if foam appears as soon as the pump starts: change the water |
| Musty or sharp smell | saturated water or biofilm in the pipework | change the water, flush the pipework, restore the AquaFinesse rhythm |
| Limescale haze or rough walls | pH too high or hard fill water | lower the pH, measure the hardness, clean the waterline |
The filter as prime suspect
A dirty filter or one that runs too briefly is the most common reason water stays cloudy while the chemistry is correct. Check:
- Run time: at least 8 hours of filtering per day, continuously if the water is cloudy.
- Pressure gauge: rising pressure means a full filter; time for a backwash or a clean cartridge.
- Valve position: the multiport valve should be on Filter; on Recirculate, the water bypasses the sand.
- Sand: after years of use, filter sand clumps together; a backwash no longer helps at that point and the sand needs replacing.
The first weeks with AquaFinesse
Anyone switching from chlorine to AquaFinesse sometimes sees slightly cloudy water in the first few weeks. That is old biofilm coming loose from the pipework, not a sign that the system is not working. Keep the filter running, clean it more often and keep to the weekly rhythm; see using AquaFinesse.
When changing the water is the only solution
- Water that stays cloudy after 48 hours of filtering with correct pH and disinfection.
- Foam as soon as the pump or jets start.
- Disinfection that disappears within a day.
- Water older than 3 months, or older than 6 weeks with intensive use.
- After illness of a bather.
The protocol is in changing the water: empty the bath, flush the pipework, clean the shell and start maintenance straight away on the fresh fill.
Prevention
- Shower before bathing: skin oils and cosmetics are the biggest contaminants.
- Keep the cover on when not in use: sunlight breaks down disinfectant and feeds algae.
- Fixed weekly dosing, never skip it.
- Clean the filter on time, even if the water looks clear.
- No soap, bath oil or ordinary fragrances in the bath; only products intended for spas.
Frequently asked questions
Why is my hot tub water milky white?
What should I do about greenish water?
Why is my water foaming?
How long does it take before cloudy water becomes clear again?
Related articles
Backwashing the sand filter: step by step, how often and what the valve positions mean
How a sand filter works, what each valve position does, the backwash and rinse procedure, how often to flush and when the filter sand needs replacing.
Changing the water: how often, when sooner and how to do it
Guideline of every 2 to 3 months, signs to change sooner, the full water-change protocol including shell cleaning and disposing of bath water in the garden.
Setting the water balance: alkalinity, pH, hardness and disinfection
Target values and the correct order for hot tub water: first alkalinity, then pH, then disinfection. With testing methods, dosing rules and common mistakes.