We’re talking about water that is cloudy, white or milky, when it is difficult to see the bottom of the pool. There are several possible causes for this problem: fluctuations in pH, algae suspended in the water, water that is too hard, or poor filtration… In any case, you need to identify the problem in order to resolve it effectively. Here are our tips.
No: These three problems have different causes and solutions, even though some of the symptoms may be similar.
In a swimming pool, if you can no longer see the bottom, it is best not to swim. In a hot tub, extra caution is required, as the high temperature accelerates the build-up of contaminants.
| eau trouble | eau blanche | eau laiteuse | |
| Appearance | opaque (often grey or greenish), so you can’t see the bottom of the pool | pale and translucent (as if milk had been poured in) | whitish and opaque (like milk) |
The good news is that you can usually restore clear water without using a whole host of products, provided you follow a simple procedure: diagnose the problem (appearance, measurements), then correct it (filter, balance, treat) according to the problem identified.
Follow these steps in exactly this order to identify the source of the problem:
| Stage | Action | Target value |
| Check the appearance of the water | ||
| Measuring pH and total acidity | test the water using ICO test strips | 7,0 – 7,4 |
| Measuring the TH | test the water using test strips | 10 – 20°F |
| Check the filtration time | check the set time | water temperature halved |
| Check the condition of the filter | check the pressure on the gauge | 0.5 to 1 bar higher than normal pressure |
How to avoid cloudy water ?
To look after your swimming pool or spa and prevent any problems, you should always stick to the three basics and follow a weekly routine:
Perform regular maintenance on your pool /spa and equipment. Here is the maintenance routine to clean your pool properly .If you have a hot tub,, read our practical guide to spa maintenance.
Whether the water is cloudy, clear or milky, and whatever the cause, regular water testing is essential. In summer, the pH should be measured at least twice a week.
A regular reading of water parameters (regularity depends on season, water temperature, number of bathers) will enable you to detect its slightest changes and be able to react before the situation becomes too problematic.
Find out more about pool water analysis
To check the various parameters, you can use test strips, electronic testers or connected water analysers such as ICO.
ICO pool is a smart device that measures parameters such as pH, disinfection levels and water temperature once an hour. Depending on how the readings change, ICO pool guides you by providing recommendations via the ICO app. ICO pool tailors its advice to the size of your pool and the treatment products you use. In this way, ICO pool saves you the hassle of common pool maintenance issues such as cloudy water, green water and overdosing…
Just like water balance, water filtration also plays a vital role
Remember this rule: the filtration time should be equal to half the water temperature. For example, 14 hours of filtration for water at 28°C.
Don't forget to check the condition of the filter (and clean it regularly), as well as the filter pressure. If the filter pressure is too high, the filter is probably clogged.
More about swimming pool water filtration or the spa water filtration
Cloudy water is one of the most common problems faced by pool owners. It is characterised by a loss of clarity, making it difficult to see the bottom of the pool or any objects submerged in the water. There are many possible causes, but chemical imbalance in the water is often the main culprit.
| Causes | Solutions |
| – water imbalance ==> presence of algae, bacteria and particles | – measure water parameters – adjust the pH and total acidity, and carry out a shock treatment |
| – inadequate or clogged filtration ==> presence of sand, dust, algae | – clean the filter – die Filterzeit anpassen |
pH is undoubtedly the primary factor responsible for water imbalance. When the pH level fluctuates, the water can become cloudy and the effectiveness of certain treatments is reduced. A pH level that is too high causes limescale and dissolved metals (iron, manganese) to precipitate. These suspended particles scatter light, giving the water a milky or cloudy appearance
Let’s imagine a swimming pool whose water becomes cloudy after a few days of hot weather and heavy use. Here are the measured values:
In this case, the water is out of balance. A high pH level reduces the effectiveness of chlorine, encouraging the growth of algae and bacteria. A TAC that is too low makes the water unstable and corrosive, whilst a lack of chlorine prevents the water from being properly disinfected.
Ineffective or unsuitable filtration is also a major cause of cloudy water. Even if the water is chemically balanced, a faulty filtration system is unable to remove fine particles, algae or suspended bacteria.
Let’s take the example of a 50 m³ swimming pool fitted with a sand filter whose flow rate is insufficient or whose filter media (sand) is clogged. Here are the signs to look out for:
White water is characterised by a whitish colour, as if milk had been poured into the pool, whilst remaining translucent. This phenomenon is usually linked to chemical issues or reactions between products. Here are the main causes, specific examples and solutions to remedy the problem.
| Causes | Solutions |
| – chemical overload following a shock treatment | – check the chlorine and pH levels – stop treatment – leave to settle |
| – a chemical reaction between incompatible substances | – check product compatibility – filter |
| – presence of metals following treatment | – use a metal chelating agent (if necessary) |
Following a chlorine shock treatment, dead white algae can float to the surface, giving the water a milky appearance. You need to act quickly to sanitize your pool. Then remove as much algae as possible with your landing net. If you use a clarifier or flocculant (see the paragraph at the bottom of the page, Difference between clarifier and flocculant, to find out which product is compatible with your filter and how to use these products) before activating water filtration.
An excess of chlorine, flocculant or other treatment chemicals can cause a chemical reaction that turns the water white.
An excess of chlorine, flocculant or other treatment chemicals can cause a chemical reaction that turns the water white.
Mixing incompatible products – highly effective anti-algae treatments containing quaternary ammonium compounds are incompatible with unstabilised chlorine and certain flocculants – can cause white precipitates to form.
Certain treatments (such as aluminium-based flocculants) or water with a high iron content can leave metal residues in suspension.
Practical example: After using an aluminium-based flocculant, if the pH is too high, the aluminium precipitates and turns the water white.
List the products used in the last 48 hours (chlorine, flocculant, algaecide, pH regulator, etc.).
Note the dosages: Overdosing (e.g. more than 20 g of shock chlorine per m³, or a double dose of flocculant) is often to blame.
Check for incompatibilities:
Algae control products containing quats (quaternary ammonium compounds) are indeed common, but must not be mixed with chlorine or aluminium-based flocculants.
Stop adding chemicals to avoid making the situation worse
Allow to settle: wait 24 to 48 hours to allow the particles to settle at the bottom of the pool
Check product compatibility: consult the product instructions to ensure that they can be mixed safely.
Filtering the water: switch on continuous filtration to remove suspended particles. If necessary, use a clarifier to clump together fine particles and make it easier for the filter to remove them.
Tester et ajuster l’équilibre de l’eau : vérifier le pH, le TAC et le TH. Un pH entre 7,0 et 7,4 et un TAC entre 80 et 120 ppm aident à stabiliser l’eau.
Clean the filter: if the filter is clogged, clean it or backwash it to maximise its efficiency.
Use a metal chelating agent (if necessary): If metals are the cause of the problem, a chelating agent can help to neutralise them and prevent them from precipitating again.
Milky water is characterised by its opaque, whitish appearance, resembling skimmed milk, with very poor visibility (it is sometimes impossible to see the bottom). Unlike white water, which remains translucent, milky water is often linked to deeper-seated issues with water quality or filtration.
| Causes | Solutions |
| – excessive limescale or scale, combined with a pH that is too high | – measure the total hardness (TH) and pH – lower the pH by adding pH- – add a limescale inhibitor if necessary – scrub the walls to remove limescale deposits. – vacuum or use a robot vacuum to remove any residue. |
| – presence of bacteria or microorganisms | – undergo an intensive treatment – check the stabiliser level – clean the filter – increase the filtration time |
| – a problem with the filtration or water circulation | – clean or replace the filter – increase the filtration time – use liquid flocculant |
| – overall chemical imbalance | – measure pH, total ammonia nitrogen (TAN), and chlorine – restore the water’s balance – undergo an intensive treatment – add a suitable flocculant – leave to infuse for at least 24 hours – vacuum up the deposits at the bottom and scrub the sides |
The presence of limescale in the water may be temporary (caused by an imbalance in the water) or linked to the water quality in your area. In this case, it is essential that you adjust your entire pond maintenance routine by using suitable products.
A total hardness (TH) that is too high (> 400 ppm) combined with a high pH (> 7.8) causes limescale to precipitate in the form of microcrystals, making the water look cloudy. This phenomenon is exacerbated by heat.
Practical example: A swimming pool filled with very hard water (TDS = 500 ppm) and poorly regulated pH (8.2) will see its water turn cloudy within a few days, particularly following a rise in temperature (e.g. after a heatwave).
Solutions
Inadequate disinfection (too low a chlorine level, a clogged filter) allows bacteria or microscopic algae to proliferate, which scatter the light and give the water a milky appearance.
Practical example: After a spell of rain or heavy use, the chlorine level drops to 0.5 ppm and bacteria begin to grow, causing the water to turn cloudy within 24 hours.
Actions to be taken
A faulty filter, insufficient flow rate or too short a filtration time (< 8 hours per day in summer) will not remove fine particles.
Practical example: A clogged sand filter (with pressure 1.5 bar above normal) no longer retains impurities, and the water becomes cloudy despite the chemical balance being correct.
What can be done to restore crystal-clear water?
An unstable pH, low total alkalinity (TAC) (< 80 ppm), or poorly stabilised chlorine disrupt the water’s balance and encourage the formation of persistent cloudiness.
Practical example: pH = 7.9, TAC = 60 ppm, chlorine = 0.8 ppm → the water remains cloudy despite several treatments.
Steps to restore crystal-clear water:
To take care of your pool or spa and prevent the water from changing too much, you should always go back to the two basics:
Generally speaking, it is not advisable to swim when the pool water is cloudy, white or milky. As always, the answer depends on how badly the water has deteriorated.
In a spa environment, the water temperature significantly increases the rate at which bacteria multiply; swimming is strongly discouraged until the problem has been resolved.
Pool or spa flocculants are used to complement water treatment (such as pH adjustment or the presence of dead white algae). They can be used when the water is cloudy, as they improve filter efficiency, disinfection and water clarity.
However, please ensure you use a flocculant that is compatible with the type of filter you are using.
Find out more at swimming pool flocculant
Both of these solutions help the filtration system designed to treat cloudy water.
Pool or spa flocculants have a binding effect that causes micro-particles to clump together, making it easier for the filter to remove them. This product requires more work and is also less water-efficient. You will need to run the pool cleaner to collect the sediment that has settled at the bottom of your pool and then top up the water level.
The clarifier removes particles via the filtration system without the need for a vacuum cleaner. Although it takes longer to work than a flocculant, the clarifier does not clog the filter with impurities and suspended particles. This product is recommended for diatomaceous earth or sand filters. It is often used following a shock treatment.
It depends on the cause (pH, limescale, a clogged filter, particles). Generally speaking, if the parameters are corrected and the filtration is effective, an improvement can be seen within 24–72 hours, though it may take longer if the filter is saturated or the water is heavily contaminated. (A useful guide, to be adapted to the specific situation)
To restore crystal-clear water, check and correct: