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A well-kept pond in the garden is not only the pride of every garden owner, but also a certain haven of peace. The quiet splashing of a fountain or small waterfall invites you to relax. In addition, it offers a natural habitat for aquatic plants, fish and other animal inhabitants. However, a beautiful garden pond is also a lot of work. Despite constant careful maintenance, it can happen that the pond water foams. The reasons for this can be quite different. More on that below.


A natural formation of foam on the water surface is quite normal. Foam usually occurs in the morning hours. It is usually not harmful. Even the movement of the water can create foam. The more water is whirled up, the higher the foam formation. This can be compared to the formation of spray when seawater moves. Imposing crests of foam can form here when there is a surf. These are all completely natural processes and not harmful. But there are also other causes for foam formation on garden ponds, such as

  • dissolved protein
  • filter problems
  • imbalanced nutrient balance
  • saponins
  • limestone
  • Surfactants from soaps, fertilizers (use of cleaning agents)

tip: Fountains, waterfalls and streams produce more or less bubbles until foam forms due to the strong movement of the water. However, this foam is not a problem.

protein dissolved in water

In most cases, natural foaming is due to dissolved protein in the water. The water contains numerous nutrients, including proteins. These flocculate through natural water movement. This creates foam on the water surface. It usually occurs in the morning, but it is harmless and indicates a well-functioning ecosystem in the pond.

filter problems

It is always necessary to ensure that the filter is properly attached and also works properly. In order to counteract foam formation, it should be noted that

  • newly installed filters initially foam water
  • need some time to break in
  • filters placed above the water surface allow more air to enter the water
  • neglected filter systems, deposits impair the function of the filter

Imbalanced nutrient balance

An excess of nutrients in the water occurs mainly in garden ponds with fish stock. Just briefly noted, these ponds are also much more expensive to maintain. There is usually an oversupply of protein here, which in turn leads to the formation of foam on the pond surface. Therefore, constant, persistent foaming is always a sign of too much protein in the water. causes are

  • fish droppings
  • fish spawn
  • rotted plant material on the pond bottom
  • foliage from surrounding trees
  • dead fish or other pond inhabitants
  • existing algae
  • Over-fertilized plants near the pond, such as riparian plants
  • Phosphate and nitrate values of neighboring agricultural properties

A rapid increase in the concentration of nutrients in the water is one of the main causes of foam on the pond. Don't forget the fish food. Part of it is taken up by the fish and the rest sinks to the bottom and rots here together with fish excrement and dead plant remains, releasing nutrients. Then there is excessive algae growth.


Also in natural waters, saponins are mainly responsible for the formation of foam in the spring. A large part of aquatic plants and also fish food contain saponins and also steroid glycosides. These are known for their typical soapy smell and taste and a function similar to soap. However, saponins are not harmful to water and pond inhabitants. On the contrary, they are helpful in the growth of the fish. However, excessive foam should be removed.

limestone in the water

Limestones placed in the water can also contribute to foaming, but less frequently in most cases. These stones enrich the water with oxygen. A larger quantity then collects on the water surface in the form of bubbles. At the same time, proteins are dissolved, which then leads to the typical foam on the pond surface. However, this does not necessarily have to be treated.

tip: Normally, pond foam is not dangerous for plants and animals, only the different causes, such as chemical substances such as surfactants or an excessive protein content in the water.

prevent foaming

Sometimes it is not always immediately apparent what is causing the foam on the pond. Before the first countermeasures are taken, a thorough investigation of the causes should be carried out. A simple removal of the foam always leads to optical problems. It is important to recognize the causes and finally eliminate them, important for healthy fish and a healthy pond environment.

tip: The water values should be tested regularly with regard to water quality (e.g. pH value, carbonate hardness, ammonium, nitrate, nitrite). Specialist shops offer suitable test sets for this purpose. Multi-parameter test strips, for example, are easy to use.

Depending on the cause, there are various options for avoiding foam formation on the pond surface, such as:

  • Foam catchers or floating barriers
  • protein skimmer
  • correct filter system and positioning
  • Eliminate protein sources
  • water change

Foam catchers and floating barriers

These are very simple devices. These are fixed in the pond near the water surface. In this way, the foam can simply be held in one place, usually at inlets, and does not drift further out into the pond. The foam can then be easily skimmed off. A piece of wood, for example, is suitable as a barrier.

protein skimmer

This module is inserted directly into the filter. Installation and maintenance is quite easy. The pumped-in water runs over various bio-rings and is simultaneously aerated with an outflow or Venturi nozzle. This results in a high surface tension due to the relatively long contact time between air and water. A solid foam is formed, which is finally separated from the clean water in the skimmer and transported away. The advantages of a protein skimmer are:

  • a promotion of protein, phosphates, ammonia, humic acid, dyes from the water
  • an improvement in the oxygen content in the water
  • a reduction in algae growth

In short, foaming decreases and water quality increases. However, this module only eliminates the symptoms, i.e. foam formation, but not the cause. In terms of price, protein skimmers range from 10 to 100 euros.

Intact filter system

For a clean pond, the filter system must always be functional. This not only includes regular care and maintenance, it must also be positioned correctly.

  • Decision for underwater filter system
  • Filter above water level: foaming is inevitable, since the returning water is enriched with oxygen to an above-average extent
  • newly installed filter systems need break-in time, about a week, initially foaming
  • additional use of pond starter bacteria in the filter

elimination of protein sources

If excessive protein content in the water is the cause of foam formation, the following measures should be taken:

  • no excessive feeding of fish, additional sources of food are plants, algae, living animals in the pond
  • Feed smaller amounts three times a day
  • Leftover food enriches the water with protein
  • remove rotted plant debris such as foliage, leaves and dead aquatic plants
  • also fish off dead fish and algae
  • regular pond cleaning
  • mainly removal of sludge layer on the bottom, contains protein-rich excrements of the fish
Fish food pond sticks

water change

A water change should always be carried out when surfactants have entered the pond. These continue to foam and pose a danger to fish and plants. this will

  • skimmed off as much foam as possible
  • much of the water exchanged
  • then let the water pump run sufficiently so that the last surfactants are removed

If there is a danger from the surrounding area. Is it recommendable

  • to stop all inflows from the outside
  • to raise the banks of the river
  • Plants along the banks and the entire garden area should be fertilized less

In general, the pond water should always be kept clean, then the protein content of the water usually regulates itself. The result is a slight formation of foam due to the movement of the water and a normal amount of dissolved proteins.

tip: Attention should also be paid to the selection of fish. Many species of fish, such as catfish (Siluriformes), form large foam nests to store the fertilized spawn for their reproduction.

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