Successfully Remove and Combat Algae in Your Pond

Successfully remove and combat algae in the pond

Pond owners are annoyed by algae because they cloud the water and consume a lot of oxygen. When the algae die, they release nitrogen compounds that promote the formation of sludge. You can use a sludge vacuum to suck out the sludge regularly. However, algae are also an indication of good water quality. A pond entirely without algae is not possible because, in the spring, they even do a good job. It is essential to combat algae effectively to prevent becoming a problem later.

Below you will learn which types of algae are most common in the garden pond and combat them.

Where Do the Algae in Your Pond Come From?

Algae begin to grow as early as spring when the ice has thawed. They can grow even at low temperatures. If the water’s nutrient concentration is expected, the algae live in peaceful coexistence with other plants and fish. The algae remove nutrients from the pond and add oxygen to the water. The algae’s living conditions improve when the phosphate concentration in the water increases. An increase in phosphate concentration of 0.035 milligrams per liter is already sufficient for this. If temperatures rise and solar radiation becomes more intense, the algae can multiply rapidly. The result of this is the so-called algae bloom. To limit algae formation, you should pay attention to the correct dosage of fish food and regularly remove leaves, branches, and other things that do not belong in the pond water. Fish feces are also a good source of phosphate. You should therefore make sure that you do not have too many fish in the pond. There are about 80,000 species of algae in the world, most of which live in the water. However, algae can also be found in the air, soil, and even snow. In the garden pond, filamentous algae, floating algae, blue-green algae, bearded algae, and brown algae are primarily found.

Filamentous Algae – A Severe Threat to Your Fish

Often found in garden ponds are filamentous algae, which belongs to the green algae. They are a positive sign, as they settle in the pond when the water quality and stability are good. They grow even at low water temperatures and can multiply even in winter. You can recognize these algae by their structure, as they form long filaments. They thrive on plants, rocks, and other objects in the pond, but they can also create algae nests that float on the water. Direct sunlight and warm temperatures provide ideal growing conditions for filamentous algae. If leaves fall into the pond in the fall and decompose, this creates an excellent nutrient base for the algae. Once the filamentous algae form a strong network with their bundles, they are difficult to remove. To prevent this from happening in the first place, you should get down to business before noticing these algae and declaring war on them. You can do this by using a landing net to skim off the algae. You can also hold a stick in the water and twist it to wind up the string algae similar to spaghetti.

The problem, however, is that the filamentous algae have developed a sophisticated survival technique. If you take the algae out of the water, vast quantities of spores enter the pond, from which new filamentous algae grow. Therefore, you cannot do without chemical aids to combat filamentous algae.

Filamentous Algae as a Risk for the Pond

Filamentous algae deprive the pond of oxygen and, when they die, leave behind nitrogen compounds. Fish and other animals in the pond can suffocate from the resulting lack of oxygen. In extreme cases, if the algae wrap itself around aquatic plants, the plants can smother. In the worst case, the water in your garden pond will tip over.

Suspended Algae – A Problem in Every Pond

Suspended algae are found in every pond and form what is known as an algae bloom. They are microscopic, but they cause the green coloration of the pond water. The tiny creatures, which float freely in the water, multiply so rapidly that the garden pond’s visual depth is only a few inches. If the floating algae are only present in a low concentration, they benefit the pond, forming an essential food base for water fleas. Through photosynthesis, these algae form oxygen. However, if they are present in a high concentration, they can become a serious problem. With the rising temperatures in spring, floating algae are already making themselves felt. They appear before the growth of the pond plants begins. The nutrients present in the pond can then not yet be absorbed by the pond plants. When the pond plants start to grow, the nutrient concentration in the pond decreases, which leads to the death of the floating algae. The pond water becomes more transparent again.

You can recognize floating algae when sunlight entering the pond reflects green, and the water appears green or brown.

Problems Caused by Floating Algae in the Pond

If suspended algae are not controlled and remain in the pond at a higher concentration for an extended period, it can cause long-term damage to the pond’s inhabitants. Sunlight can no longer reach the aquatic plants due to the turbidity of the water. Photosynthesis is then only carried out weakly or not at all by the water plants. As a result, the aquatic plants die. The dying of the plants creates a vicious circle. The dead plants are no longer food competitors for the floating algae, but they still provide nutrients. More sludge is formed in the pond. Fish and other animals may die. If the suspended algae occur in excessive numbers, they can throw the pond water out of balance. In a single night, the oxygen level in the pond can drop to zero. As a result, all life in the garden pond suffocates.

How to Get to Grips With Floating Algae

There are several ways to combat floating algae:

  • Strongly growing pond plants that serve as food competitors and remove nutrients from the water. Hornwort or waterweed works well.
  • For larger ponds, carp that feed on suspended algae are suitable. – However, you should not have too many fish as they may eat the pond plants. The fish feces serve as nutrients for various types of algae.
  • UVC pond clarifier, the algae absorbs those ultraviolet radiations, and their internal structure gets destroyed.
  • Chemical agents to control the algae.

Blue-green Algae With a Slimy Structure

Blue-green algae are present in the garden pond throughout the year and can multiply if sufficient nutrients are available. They belong to the most robust algae species. They are not algae at all, but cyano-bacteria, which resemble algae, can be recognized by their slimy structure. If they occur in a higher concentration, for example, they can also become dangerous for humans in a swimming pond. Blue-green algae usually float on the water surface, but they can also form furry coatings on water plants. On the water surface, they can create an oily film on which bubbles sometimes appear. This film can mutate into a carpet up to 5 inches thick that settles on the bottom of the pond. The blue-green algae emit a very unpleasant odor.

Blue-green algae can indicate excessive nutrients in the water. Excessive feeding, but also too many fish, can be the cause. If your fish has increased, you should not kill the excess fish. You can give them away to other pond friends or trade them for aquatic plants at a swap meet. Blue-green algae can also indicate too high an ammonium concentration in the pond, which occurs when biological filtration is not working correctly.

Blue-green Algae as a Risk for the Pond

Because blue-green algae emit toxic substances, they can become even more dangerous to your pond than other algae. If these toxins accumulate in the fish, it leads to mucous membrane damage and other fish’s health problems. The blue-green algae can also harm other animals. Eventually, pond inhabitants die, as well as microorganisms. Your pond gets out of balance.

Bearded Algae With Coherent Structures

Bearded algae are also known as red algae or black spot algae, and they form interconnected structures. Because they develop long stolons, they are often confused with filamentous algae. A weak flow through the pond and a low level of CO2 promote the formation of beard algae. Ideal conditions for the beard algae are too high fish stocking or excessive feeding of the fish. Beard algae can settle on the pond plants and are difficult to fish out.

Brown Algae – A Frugal Species

Brown algae get by with little light and few nutrients. They, therefore, find the right growing conditions even in deeper pond zones. They often appear on stones and pond walls and can be recognized by their brownish to reddish coloration.

How Can You Act Against the Algae?

To successfully combat algae, you should identify and address the cause of the algae. You can achieve this with fewer fish, less feeding, or more water plants. A pond filter will do a good job. It would help if you did not do without a mud vacuum cleaner to make your pond fit for the winter. It works best if you combine a mud vacuum cleaner with a filter. If many mulm forms in your pond, you can also use the mud vacuum cleaner in between. If many algae have settled in your pond, you can use biological products in the form of powder or liquid to combat the algae. To counteract the formation of algae, you can use several creative ideas:

  • Covering the pond with a net in the fall. If you do so, not much foliage ends up in your pond.
  • Shading the pond with a sun sail so that the sun’s rays are not too intense
  • Fountain, which provides constant water movement
  • Oak branch in the water, which gives off tannins and lowers the pH. However, it would help if you took out the oak before it decomposes.


The most common algae types in the garden pond include filamentous algae, floating algae, and blue-green algae. Blue-green algae are not algae but bacteria. The bacteria release toxins and are thus a significant threat to your pond and the pond inhabitants. Algae remove nutrients from the pond and can severely disrupt the balance. You should remove algae as soon as you notice them. You can do this with biological algae removal products, filters, and mud vacuums.

Florian Egert

I am Florian Egert, the owner of I live with my wife and two children in Germany in a small village in the countryside.

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