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To rid the pond of elders, you do not need to resort to chemical means. An old home remedy for fighting algae is cow's milk. This is an effective alternative to chemicals, especially in natural ponds.

In a nutshell

  • Lactic acid bacteria can reduce algae
  • Cow's milk contains only small amounts of lactic acid bacteria
  • Cow's milk can promote algae growth due to other ingredients such as fats or lactose
  • Alternatives, like whey, have a better mode of action
  • Constantly check the pH value to prevent acidification of the water

Causes of Algae

Algae form in the pond when the balance is no longer right. As a rule, there are microorganisms responsible for the self-cleaning of the pond, which include other lactic acid bacteria. However, if the nutrient content in the water increases, combined with heat, these organisms will eventually be overwhelmed and the water will tip over.
If the nutrient content in the water is too high, algae suddenly start to multiply. Standing waters in particular are often affected and filamentous and floating algae multiply in them. A small amount of different types of algae does not harm the inhabitants of the pond, but if the algae load is too high, this can lead to clouding of the water, which affects not only the pond inhabitants but also aquatic plants.

Notice: The turbidity in the water reduces the incidence of light. As a result, aquatic plants can carry out less photosynthesis and die off in the long term.

use lactic acid bacteria

Lactic acid in concentrated form is already available in specialist shops as a means of combating algae. However, commercially available cow's milk contains only a few lactic acid bacteria and is therefore only of limited effectiveness. Occasionally, milk even exacerbates the problem because the protein and fats it contains can be additional food for algae species.
Raw milk has a slightly higher content of lactic acid bacteria. The content of lactic acid bacteria can also be increased if you leave the cow's milk in a warm place for a few days.

apply milk

The use of cow's milk as a means of combating algae is controversial in terms of its mode of action. You should therefore always proceed with caution when using cow's milk.
Preferably use raw milk, which you use as follows:

  • Leave the raw milk in a warm place for a day
  • Skim off the fat on the surface of the raw milk
  • Pour the raw milk into the water in a ratio of 1:2500
  • Lightly stir in the raw milk

For a small tank, one liter is usually more than enough. If you only use a water barrel or an even smaller container as a mini pond, you should add a maximum of one small glass of raw milk to the water. With such small water vessels, it sometimes even makes more sense if you approach the ideal content with small amounts. This also applies if you do not know exactly how much water your pond holds.

Alternative dairy products

Instead of using cow's milk to combat algae, it is advisable to use dairy products with a higher concentration of lactic acid. An alternative is sour whey, which is produced when the milk coagulates with the help of lactic acid bacteria. The advantage is that there is practically no more fat in the whey and the lactose is also significantly lower. On the other hand, the acidity is higher, which may have a negative impact on the pH value in the pond.
When using whey, proceed as follows:

  • Check pH
  • add whey when the pH is above 8
  • Mix whey in a ratio of 1:2000
  • Check pH again
  • should not fall below 7.5
  • check again after 2 days
Check pH

Algal blooms are promoted, among other things, by a very high pH value. With the acidic whey, you can not only fight the water algae, but also lower the pH value at the same time. This can also reduce the growth of algae. Often this is even enough to combat the algal bloom.

Notice: An advantage of whey is that it is not cloudy like cow's milk, but almost clear. This does not additionally reduce the incidence of light in the water.

frequently asked Questions


Can I use milk from other animals?

Yes, lactic acid is also contained in sheep's or goat's milk. You can therefore also use other types of animal milk.

How warm does the water have to be?

Lactic acid bacteria need a temperature of at least 8°C so that they can multiply.

How often can I use milk products against algae infestation?

Before using the product again, wait at least until the cloudiness of the water caused by the cow's milk has disappeared. Also observe whether the milk improves or worsens.

Can I gradually optimize the pH value with lactic acid?

Yes, it is actually much better for the organisms in the pond if you gradually lower the pH value if it is too high.

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Garden design