If there is one thing above all others that can dampen the mood of any pond owner, it is having too much algae in their pond. We take a look at the most common types of pond algae  and explain how you can combat them.

As one of the simplest forms of plant life, algae are particularly widespread. Although they serve as a form of food for many animals, this is of little comfort to pond owners when unsightly, brownish-green ‘mush’ covers the pond floor, clumps of algae float around unattractively or suspended algae turn their water murky.

However, their unsightliness is not the only issue caused by algae plagues. Excessive algae in ponds  also poses a further risk: they can cause such drastic changes to certain water parameters, such as the carbonate hardness and the pH value, that a hazardous lack of oxygen can ensue, especially in the mornings.

To combat an algae plague in your pond, you first have to look at what caused it. This is the only way to enjoy permanently clear water. Excessive algae growth is almost always caused by too high a nutrient content in the pond (e.g. of phosphate or nitrate). Please note that the nitrate and phosphate levels in a pond can, however, be perfect despite an algae plague. This is because the algae consumed these nutrients to spread in the first place.

For more about ideal water parameters, please see the article ‘The most important water parameters in ponds’.

When it comes to algae in garden ponds , the following basic differentiations are made: 

Green algae in ponds

Green algae in ponds are particularly common in spring. Such algae include filamentous and suspended algae. The increase in sunshine offers green algae good conditions for growth, especially as the other pond plants do not yet provide any real competition for the nutrients in the water. 

Filamentous algae in ponds 

Filamentous algae generally need good water quality and tend to develop gradually: they can be free-floating and drift around the pond in large clumps or in the form of filamentous tufts attached to the pond floor, plants or pieces of equipment. 

Suspended algae 

Suspended algae cause green pond water. For more about what causes these algae in ponds and how to combat them, please see the article ‘Suspended algae turn pond water green’.

Blue-green or smear algae in ponds 

Although blue-green algae can also be found in suspended form, they usually appear as an unsightly slimy covering on equipment and the pond floor. Blue-green algae are unpleasant contemporaries that particularly thrive in poor water quality, especially in the case of very high nitrate and phosphate levels. To avoid blue-green algae, you should look after your pond carefully.

Depending on the type of algae found in a pond, there are several ways to combat them. For example, filamentous algae can be either fished out or reeled in. The pond and its water can be cleaned using a net or a rake (be careful not to damage the pond lining!). Sometimes, the algae can be simply reeled in by winding them around a stick.

Algae eaters in ponds 

Certain animals assist you in your battle against pond algae. These include small crustaceans, water snails, pond mussels and several species of fish. However, you should not expect miracles. In addition, these little ‘helpers’ many also cause problems of their own in the pond.

Anti-algae agents

Although chemical-based anti-algae agents should not be used as a long-term solution for combating algae, several premium quality and brand products are now available on the market for use on a temporary basis. These agents are also fully recommended as emergency measures. When using them, however, please remember that, even with the best products, you will not achieve lasting success if you do not properly maintain your pond and prevent new algae plagues. 

Plants that compete with algae 

Stocking a pond with plenty of pond-side and underwater plants is one of the best ways to combat algae. This is because floating and underwater plants use up the nutrients in the water so they are no longer available to the algae. Plants like hornwort, waterweed and water soldier have proven to be particularly good choices, as have reeds planted in the gravel around the edge of the pond.

Full decontamination to combat pond algae 

Full decontamination of a garden pond should not mean that the pond is completely emptied and then cleaned with a pressure washer, for example. This would cause both huge disruption for the pond life and lasting damage to the pond’s ecosystem. If sediment or poor water parameters are causing major problems, however, extensive maintenance measures can be vital to the pond’s survival. Removing the sediment and conducting several large partial water changes helps unhealthy ponds to recover. These maintenance measures can be conducted quickly and easily. Note: keep an eye on hot weather as this can cause ponds to dry out.

The battle against algae in ponds is not always one that can be won overnight. Keep at it! For example, this means regularly fishing out dead plant matter, leaves and flowers. And above all: use appropriate pond care measures to prevent new algae infestations. 

For more information, please see the article ‘Winter-proof your pond in autumn’.

The following tips can also help you in the fight against algae: 

• In summer, don’t just top up your pond with tap water; also conduct partial water changes
• Is the water temperature too high in summer? Then it is important to sufficiently aerate the pond
• Do too many fish live in your pond? Reduce the stock of fish and always use high-quality food to avoid contaminating the water
• Ensure that substances that shouldn’t be in your pond are unable to get into it (e.g. fertiliser for land plants)