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Nobody wants to swim in a pool where not even the bottom is clearly visible. If the pool water is milky, it doesn’t look very inviting.

However, cloudy pool water can also be an indication of dangerous bacteria in the pool. The bacteria can harm the pool, the pool equipment and also the health of the bathers.

In this article, we discuss the reasons why a pool becomes milky, what the turbidity indicates, and how to solve the problem once and for all.

The costly damage and health risk to bathers can only be avoided if the cause of the milky pool water is identified and properly treated.


Let’s jump right in with the possible causes.

Pool milky or cloudy: The possible causes

It is possible that overnight the pool water becomes cloudy milky or green.

Normally, however, turbidity does not develop from one day to the next.

Often, this is a long-term process. At first, the slight cloudiness may not bother you at all, but after just a few days, the problem is unmistakable.

Those who do not act immediately will soon have a bigger problem.

Cause #1: The filter system is not working properly

A common cause is the filter system. If problems occur here, the water can become cloudy, making swimming in the pool dangerous.

In regular operation, the pool filter should run at least eight hours a day to keep the amount of debris to a minimum. Together with the various disinfectants, the filter system keeps all impurities out of the pool.

However, the filter system must be maintained – just like the pool itself. It is important to clean the filter thoroughly and replace the cartridges regularly. This ensures that the filter works smoothly.

A filter system also ages (and not very well).

Failure to remove contaminants from the pool will result in increased consumption of pool disinfectants (such as chlorine). The organic material in the pool in turn attracts more bacteria, which leads to more contamination. As a result, splashing in the pool can also be dangerous for the bathers.

Cause #2: Too little disinfectant

An important part of pool maintenance is the use of disinfectants such as chlorine. These chemicals attack foreign bodies, but are not designed to handle large quantities of solids.

The larger particles are normally filtered out by the filter system. However, if the system does not work properly and you do not additionally help with a pool vacuum or a landing net, the disinfectant will be used up within a short time.

When bathing, skin flakes, sunscreen, the remains of body and hair care products, but also body fluids such as sweat get into the pool.

The consumption of disinfectants is thus directly related to the use of the pool. Algae in the pool also increases the need for chlorine or other pool chemicals.

In addition, disinfectant is steadily degraded by solar radiation. The UV rays break apart the hypochlorite ions that form when the pool is chlorinated. The broken ions simply evaporate into the air.

Chlorine and other disinfectants keep the pool clean by binding organic debris. The more impurities that enter the pool, the more chlorine is bound and, as a result, the need for disinfectants increases.

The loss of effective disinfectant then favors the colonization of algae as well as bacteria and pathogens such as E. coli in the pool. This makes the pool water look milky, but taking a dip in the pool can also be hazardous to your health.

Cause #3: The pool chemistry is not in balance

Every pool owner should have a basic understanding of pool chemistry. Because with a pool that is not chemically in equilibrium, it is more a matter of when, not if, the pool becomes milky white or cloudy.

Unbalanced pool chemistry leads to milky pool water, but that’s just one of the smaller problems.

Other consequences are health risks while bathing, corrosion and damage of pool accessories and extensive pollution of the pool.

Pool owners need not be surprised if, without their care, the crystal-clear pool water turns into a murky mess within two to three weeks.

The causes of turbidity of water can also be too high pH, particularly high calcium hardness, high alkalinity and even a lot of chlorine. Shock chlorination of the pool can also temporarily make the pool water appear milky murky.

5 Problems of milky pool water

The reasons why the pool water becomes milky are now known. But is that a problem?

The turbidity is not pretty, of course, but often the turbidity of the water is a symptom of more serious problems.

1. too high chlorine content

Excessive chlorine concentration may cause lung and skin irritation. This is particularly dangerous for people with respiratory diseases such as asthma or bronchitis.

Chloramines are formed as a by-product of chlorinating the pool and also have an irritating effect. In addition, chloramines can also cause corrosion.

2. algae in the pool

Often, cloudy pool water is a sign that algae is growing in the pool.

Most often, algae that spread in swimming pool are not dangerous to health.

However, the suspended solids that form from the dead algae cause the pool water to become very cloudy.

Highly turbid pool water poses a high risk to animals and small children. When there is a lot of dead algae in the swimming pool, you can often barely see the bottom. Animals or small children falling into the pool can thus no longer be detected.

Another problem is that animals do not even recognize a heavily polluted pool as such. This causes them to fall into the pool more often.

Until the problem with turbidity is solved, it is best to block access to the pool for children and pets.

3. many bacteria in the pool water

A cloudy pool may also indicate that bacteria and other pathogens, such as E. coli or Legionella, may be present and multiplying in the pool.

After all, the pool water often becomes cloudy because there is not enough disinfectant in the pool. (There are several reasons for this).

4. ineffective filter system

In the event of a complete or partial failure of the filter system (e.g. due to clogging), the pool water may become cloudy.

If the filter pump is not operated at least eight hours a day, debris can build up in the pool and cause the water to appear milky over time.

The debris that is not filtered out also provides for higher chemical consumption, which in turn encourages bacteria to proliferate.

5. pH value too high

Anyone measuring a high pH in the pool had better take action.

Alkaline pool water promotes algae growth as well as can lead to calcification of pool walls and wear and tear of metal and vinyl.

As a result, the filter system may also become clogged, clouding the water even more.

6. heavy metals in the water or too high alkalinity.

Pool water with high alkalinity can attack the metal and cause wear to the vinyl.

Calcium, on the other hand, is the cause of scaly deposits that cloud the water and clog the filter. Heavy metals such as copper or zinc can have a similar effect.

The solution: Clear the pool again (step-by-step guide)

If the pool water appears milky or cloudy, it may be a sign of serious problems.

Now it’s time to get the pool clean and the water crystal clear again.

Step 1: Basic cleaning

The first thing on the schedule is a basic cleaning of the pool. A pool brush is used to clean the walls and floor.

For pools made of concrete or plaster, pool bristles with steel bristles are the better choice.

In contrast, vinyl pools use only brushes with bristles made of the softer material nylon. (This is because the hard steel bristles could damage the plastic).

Step 2: Vacuum the floor

The larger deposits, which have now been brushed off, are subsequently removed with a manual pool vacuum or battery pool vacuum. (This is because the skimmer does not manage to suck in the sediments from the bottom).

Alternatively, a pool robot can be used to remove debris automatically.

Step 3: Shock chlorination

Shock chlorination effectively kills algae, bacteria and other organic material in the pool. The highly concentrated chlorine has a disinfecting effect.

The active chlorine in the pool shock decomposes when exposed to sunlight, so it does not have a major impact on the chlorine balance of the pool.

If the pool is heavily infested with algae, it must be shocked several times.

More about this, we have reported in our article on home remedies for algae in the pool.

Step 4: Filter thoroughly

With the filter system, the pool shocker is distributed throughout the water circuit of the swimming pool. Normally, the filter should run for at least eight hours a day. This ensures that all the water is circulated once a day.

The filter system also requires regular maintenance. Before filtering can begin, the cartridge of the filter should be replaced or the pool filter should be flushed with filter cleaner.

Step 5: Test water quality and restore balance

When the pool no longer looks milky and the pool water looks clear again, it’s time to test the pool water.

A test kit or test strips can be used to examine the water more closely.

Pool chemicals are added to the water as needed to rebalance the pool chemistry.

Quick tips: What helps against cloudy pool water?

  • If the turbidity is not so strong, flocculant already helps. The chemical causes fine particles to combine into lumpy deposits and sink to the bottom. A pool vacuum cleaner can be used to cancel them afterwards. During suction, the water is discharged from the pool as wastewater.
  • If you clean your pool regularly and thoroughly, you will rarely have to deal with milky pool water. Key responsibilities include testing the water pool water weekly and keeping the pool chemistry balanced, as well as removing debris and other dirt from the pool on a regular basis.
  • Water clarifier does not solve the problems mentioned above, but should be added to the pool as part of weekly water maintenance. The agent ensures that the water in a (well-maintained) pool remains crystal clear.
  • When the pool is not in use, it should be covered with a pool tarp. This is especially important if you want to winterize the swimming pool. In this way, foreign bodies can not get into the pool at all.
  • Leaves and other coarse debris will not be collected by the filtration system or by a pool robot. Remove these contaminants from the water with a landing net or pool vacuum. This makes the filter’s work easier, reduces the need for chlorine and is therefore also easy on the wallet.

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Die Redaktion von Wellenliebe.de besteht aus echten Wassersport-Fans. Von Kajakfahrern, über Segler und Taucher bis Stand Up Paddler sind (fast) alle Wassersportarten vertreten. Unsere Inhalte wurden schon millionenfach gelesen und in vielen Zeitungen aufgegriffen.

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