Duckweed: How to Remove and Prevent it

Duckweed is easily recognisable; it consists of a small, pea-sized green flowers with small roots reaching below it. In summer, Duckweed can be a big problem as Duckweed flowers can double in size every few days. It is very difficult to prevent; as it can get access to your pond via plants, birds, frogs or from new fish from a different pond.

Duckweed is often found in ponds that have a lot of nutrients; particularly Ammonia, Nitrites or Nitrates. These chemicals are often caused by a build up of debris on the bottom of the pond; this normally indicates that there is either a problem with your filtration or that there is a lot of debris getting into the pond which your filter can’t remedy.

The below blog will look at whether Duckweed is harmful to your fish and the three different ways in which the Duckweed can be treated.

Is Duckweed harmful to fish? (Useful Blogs: Duckweed: Friend or Foe)

A controlled amount of Duckweed in a pond can actually be beneficial as it can aerate your pond; but it will become problematic if your pond has too much Duckweed. If you experience uncontrolled Duckweed growth, you should resolve it quickly. Excess Duckweed can kill off the ecosystem by reducing the oxygen levels and sunlight available to your pond. This can kill any fish, frogs and plant life. 

Prevention (Useful Blogs: Aeration, Pond Sludge)

There are natural ways which can either prevent the development of the Duckweed or control its development. This method will always rely on you controlling the chemicals in your pond; so regular testing using either the Tetra 6-in-1 Test Kit or the Blagdon Pond Health Test Kit.
• Prevent sludge from building up as it can cause a chemical imbalance.
• Install a cover net on your pond to stop any leaves and other debris from falling in and also removing any excess plant growth from your pond in the winter months.
• Duckweed prefers stagnant or slow-moving water; so install a fountain or a waterfall to keep your water circulated and aerated.
• Add extra oxygen into your pond through an air pump, which will vastly improve the water quality.
• Adding fish into your pond may also help to control the Duckweed, as they will it. Goldfish seem to love the taste of Duckweed!
• Avoid over-feeding your fish and over-fertilising pond plants in the pond.

Mechanical Control

Mechanically controlling the levels of Duckweed in your pond will include manually removing the Duckweed with a fine net, vacuum or another manual method. The best techniques we have heard include:
• Wait for a windy day, where the wind will blow the Duckweed to a specific part of your pond; making it easier to remove.
• Install a Waterfall, which pushes the Duckweed to the opposite site of the pond. Waterfalls are great as they disrupt the surface of the pond, which Duckweed doesn’t like!
• Install a pond skimmer on your pond, like the Pondxpert SkimmTrio 36. The Skimmer attracts all surface debris and collects it, allowing efficient pond surface maintenance.

Chemical Control

Alternatively, you can manually remove as much Duckweed as possible with a net and then use a chemical treatment like PondXpert-Anti Duckweed or Blagdon Duckweed Buster.

If you have any queries, please do not hesitate to email us on info@pondkeeper.co.uk.