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Duckweed: How to Remove and Prevent it

Duckweed can be beneficial in controlled amounts, but deadly to a ponds ecosystem when it is uncontrolled.

06 October 2020

Duck Weed: Friend or Foe?Duckweed is an easily recognisable problem in ponds; it consists of a small, pea-sized green flowers with small roots reaching below it. In the summer months, Duckweed can be a real problem for ponds as the number of Duckweed flowers can double in size every few days.

Duckweed is very difficult to prevent; as it can be introduced into your pond with plants, birds, frogs or when you are introducing fish from a different pond.

Duckweed is often found in ponds that have a lot of nutrients; particularly ponds with a build-up of Ammonia, Nitrites or Nitrates. This chemical imbalance is 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. You may also want to look at another blog post on our website; Duckweed: Friend or Foe.

Is Duckweed harmful to fish?

A controlled amount of Duckweed in a pond can actually be beneficial for the pond; the individual plant can help to oxygenate your pond; but it will become problematic if your pond has too much Duckweed.

If you do experience uncontrolled Duckweed growth, it is important that this is resolved as quickly as possible. An uncontrolled level of Duckweed can kill off the ecosystem of the pond, killing any fish, frogs and plant life. Duckweed does this by developing rapidly, covering your pond and reducing the oxygen levels and sunlight available to your fish.

pondxpert electroair compact 2400Prevention

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.

You will also need to prevent any debris from building up; as this debris can cause a chemical imbalance. So this means having 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; this is why having a fountain or a waterfall in your pond will help to act as a control mechanism for Duckweed. You can also add extra oxygen into your pond through an air pump, which will vastly improve the water quality; I would recommend checking our aeration blog.

Adding fish into your pond may also help to control the Blanketweed; fish like Koi and Goldfish will eat the Duckweed, which provides some form of control. Goldfish seem to love the taste of Duckweed!

pondxpert skimmtrio 36 - pond skimmer with fountain optionMechanical 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 is to either:

  • Wait for a windy day, where the wind will blow the Duckweed to a specific part of your pond; which makes it easier to remove
  • Install a Waterfall in your pond, which will push the Duckweed to the opposite site of the pond. A waterfall is really good as it disrupts the surface of the pond, which Duckweed doesn’t like!
  • Install a pond skimmer on your pond, like the Pondxpert SkimmTrio 36. The Skimmer will attract all surface debris and collect it inside the Skimmer; allowing efficient pond surface maintenance.

 pondxpert anti-duckweed 1,000mlChemical Control

After manually removing as much Duckweed as possible, you can then use a chemical treatment to PondXpert-Anti Duckweed or Blagdon Duckweed Buster.

It is also important to avoid over-feeding your fish and to avoid over-fertilising pond plants in the pond.

If you have any queries, please do not hesitate to contact us.

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