Algae in the pool - how to fight the green plants

the essentials in brief

Algae are formed when the pH value, nutrient content and heat are too high
Chlorine and regular water cleaning prevent infestation
Algae can be combated with chlorine, algaecides, hydrogen peroxide or hydrochloric acid

Different types of algae in the pool

Algae belong to those plants that can have one or more cells. They need sunlight for their growth, which is why algae only grow in exposed areas. The organisms are very undemanding and use CO2 and the sun as energy suppliers to produce carbohydrates and oxygen. There are particularly stubborn algae.

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	scientific	Occurrence	Hints
Red seaweed	Rhodophyta	Littoral zone of the sea	Bacterial film in pools is mistakenly called red algae
Brown algae	Phaeophyta	almost exclusively marine	resistant organisms with a filamentous structure
Green algae	Chlorophyta	over 50% of the species live in fresh water	form suspended particles or long threads
Yellow algae	Xanthophyceae	Freshwater	often referred to as mustard algae
Black algae	Cyanobacteria	predominantly in fresh water	no algae; take root in plaster of paris and concrete

Alleged white, red and black algae

If shimmering red or black spots form on the pool walls, it is usually not caused by algae. It is a bacterial lawn caused by environmental influences and a lack of disinfection. Occasionally these bacterial accumulations can also be colored white. The patches separate from the primer and then float in the water. Sometimes deposits that come from outside and settle on the bottom are also mistaken for algae.

Cause of algae growth

The pH value and the color of the water provide information on the water quality and indicate which cleaning measures are necessary. Ideally, the pH value is 7.4. Algae feel good at higher values. Algae and bacteria are not always responsible for discolored water or deposits on the walls:

yellow-green water : indication of increased iron concentration
Milky water : pollution from organic residues
Slippery walls : algae or bacterial lawns
rough pool walls : calcification of the water

How do algae develop in the pool?

If there is not enough algae protection in the pool water, the risk of algae growth increases. The pH value also has an influence on algae growth. The organisms need nutrients to grow, which they get from leaves, hair, cosmetics or skin flakes.

Are algae dangerous?

Algae in pools pose no health risk. Despite the unsightly color of the water, you can swim in the water without hesitation. However, the algae growth should not get out of hand, because some species then produce substances that are toxic for humans. This is especially true for cyanobacteria. They produce secondary metabolic products that they do not necessarily need for their actual growth.

Digression

Algal bloom

Increased temperatures in combination with over-fertilization of the water with phosphate can lead to so-called algae or water bloom. This describes a sudden and massive increase in algae and cyanobacteria. Depending on the species, the water surface turns green, red or blue. The water becomes heavily clouded and only little light reaches the lower layers. Some algae and cyanobacteria produce toxic substances that can be dangerous for bathers. However, there are only around 50 species of algae that develop such toxins.

When do algae form in the pool?

Algae grow where the water circulation is low. Heat and changeable weather as well as residues in the water favor the development of algae. Therefore, algae growth mainly occurs in spring and summer. The most common types of algae in pools are green algae. Brown algae show up as deposits on the pool floor and on the walls. Yellow algae occur less often and develop a powdery precipitate on the ground. Bacteria arise as a result of a lack of cleaning routine on the walls or on the floor.

Remove and fight

Fighting algae successfully usually requires chemical agents. This pollutes the water and there are health risks if the dosage is incorrect. So that it doesn't get that far in the first place, you should prevent algae growth with the right water treatment.

Basic principles of proper cleaning:

Remove coarse soiling with a net
Vacuum the walls and floor
mechanical water treatment with pumps and filter systems
chemical water treatment
Water exchange by submersible pump

Algae in the pool are not dangerous. However, they indicate an imbalance.

chlorine

Chlorine is the classic disinfectant in swimming pools. It prevents algae and bacteria from multiplying and kills them. Chlorine can also be used in the presence of algae. The concentration should be around three parts per million. If you have algae in the pool despite chlorine, various factors can come into question:

insufficient water flow
Foils act as flow brakes
chlorine concentration too low

Algicide

These biocides are effective against the formation of algae. If it is used regularly, it can have a preventive effect. If the pool is already infested with algae, these agents usually no longer help. The organisms multiply despite the algicide. Many algicides are high in metals, which can lead to further problems. If you still want to use these biocides, the agents should be free of copper.

Copper sulfate

Copper is a powerful agent that stops most algae from growing. Copper sulfate used to be the main component of algicides. Today it is only used sporadically. It also kills the extremely resistant black algae on the walls. However, it also has disadvantages. Pool water that has been treated with copper sulphate must not be drained into the sewer system. It must be disposed of properly, as the heavy metal is harmful to aquatic organisms.

Bacteria and viruses are not killed
Algae can develop resistance
increased copper content for black spots or yellowish discoloration

Hydrogen peroxide

An alternative to chlorine is water treatment with active oxygen. If hydrogen peroxide is added to the pool water, under UV radiation, hydroxyl radicals are formed. These have a much stronger effect than the peroxide and ensure the breakdown of organic impurities. The disadvantages are that the water can quickly become unbalanced. This is especially the case in the high season. If chlorine and hydrogen peroxide are used at the same time, the water can become cloudy and a water exchange is necessary.

hydrochloric acid

Acids are used to lower the pH value and curb the growth of algae. Hydrochloric acid is a highly corrosive liquid that should not be used in private pools. Another disadvantage is that chlorides get into the water with the hydrochloric acid. These can promote corrosion.

Unsuitable means

There are some home remedies that shouldn't be put in the pool. Either they are not effective or they are not used to remedy the algae problem. So think over your methods well in advance and weigh the potential dangers against the benefits.

vitamin C

Ascorbic acid briefly ensures that the water that has been clouded by algae appears clear again. This phenomenon is based on a chemical reaction that makes iron particles invisible. Vitamin C is not able to remove these particles or to fight the algae. The basic problem is still there, which is why this home remedy is not suitable for combating algae.

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soda

Washing soda or sodium carbonate can be added to pool water to raise the pH level that is too low. About five grams of soda are required per 1.00 liter of water to increase the pH value by 0.2 points. However, this measure cannot combat the growth of algae, as algae prefer to live in water with pH values above 7.5. Soda should not be confused with baking soda, because it is sodium hydrogen carbonate.

Home remedies for algae in the pool

Cleaning the pool without chemicals is good for your health. Since water is sensitive to the addition of various agents, the correct dosage is extremely important. The most successful weapon in algae control is fresh water. A complete water exchange is useful in the case of strong algae growth.

salt

Many pool owners use table salt to destroy algae. Slightly salty water not only has an antiseptic effect, but can also kill freshwater algae. For this reason, salt systems are used that work with a salt concentration of 0.4 to 0.7 percent. The addition of table salt can also be used to combat algae. However, over time, the salt attacks metallic objects and in the worst case all the water has to be replaced.

vinegar

Just like citric acid, vinegar is a natural agent that can lower the pH value. With the consumption of oxygen, acetic acid breaks down and salts remain. As a result, living beings in the water can be killed if sufficient water circulation is provided. The downside is that vinegar can encourage bacterial growth.

Tips

At the pharmacy, you can buy test strips that you can use to test the pH.

Water treatment

To prevent algae growth in the first place, the water must be cleaned and treated regularly. After the winter season, the pool should be cleaned thoroughly so that no residues affect the water. It is just as important to regularly add fresh water to the pool. The older the water, the higher the risk of algae formation. Since the organisms need light to grow, an opaque tarpaulin is necessary as a cover. Remove corroded objects and dead organic material

pH should be between 7.0 and 7.4
The ideal chlorine value is 0.3 to 0.2 milligrams per liter
Check values weekly

Tips

Before going on vacation, give a chlorine shock to kill organic compounds and bacteria.

Sand filter

A correctly dimensioned sand filter system cleans the entire pool water with the help of sand with a grain size of 0.5 to 0.8 millimeters. If the water is pumped through the filter system, small suspended particles remain and the water enters the pool clean.

So that the filter performance is not impaired, the dirt must be backwashed in the drain. The dirt particles are flushed from the filter into the wastewater. This process should be repeated every week to prevent particles from building up in the water. The quartz sand (€ 14.90 at Amazon *) should be renewed every two years.

Cartridge filter

These filter systems are an alternative to sand filters, which are equipped with a paper cartridge. Here too, dirt particles are removed by pumping the pool water through the filter. In order to remove the filtered out particles, the cartridge has to be hosed down or changed. Leaves, small stones or sand are not filtered out and must be removed with a pool vacuum.

frequently asked Questions

What causes algae in the pool?

Algae are plant organisms that need nutrients, warm temperatures and sunlight to grow. You feel good at higher pH values above 7.5. If the concentration of disinfectants in the water decreases and the environmental conditions are optimal, algae can form overnight in spring and summer.

Algae in the pool and still bathe?

Most of the algae that settle in the pool are neither harmful nor toxic nor dangerous. Only a few types of algae develop toxic substances during the algal bloom when they multiply in large numbers. The bacteria, which are often mistaken for red or black algae, are also harmless. You can swim in the water without any problems. The only danger is the cloudiness of the water caused by green floating algae. They obstruct the view when diving.

What helps against algae in the pool?

The floating threads should first be removed with the net. Algae and bacterial lawns must be mechanically removed from the walls and floor, as these can sometimes develop stuck roots. Measure the water values to determine whether they are in the normal range. Shock chlorination is effective in combating algae. A water change is recommended in the case of strong growth. Also remember to clean all filter systems.

What can be done against algae and worms in the pool?

When ambient temperatures rise, algae and small red worms can suddenly grow. The mosquito larvae hide behind the worms and prefer to lay their eggs on the water. These creatures cannot survive if the water is appropriately disinfected. Chlorination can help. The filter systems should also be checked and cleaned if necessary.

Why do I have dead algae in the pool every day?

Flocculants are added to the skimmer as they bind the finest dirt particles. It is placed in the skimmer, which should run until it is completely dissolved. If it is switched off, the agent can flocculate in the water. As a result, structures can form in the water that are reminiscent of white algae. If green algae appear regularly, consider a short-term chlorine shock.