Duckweed (Lemnoideae) is by far the most controversial plant in the aquarium hobby. It is considered by many to be a pest and has been referred to as the ‘herpes’ of aquarium plants. However, Duckweed can have many benefits and can contribute to the stability of the planted aquarium.
Duckweed is the smallest floating plant in existence. It thrives in still water environments and does not do well in fast flowing waters. Although Duckweed can reproduce through sexual reproduction, most of the time it reproduces using asexual reproduction. Using asexual reproduction this plant is able to rapidly populate almost any environment.
Duckweed and Algae
Keeping Duckweed in your aquarium is an excellent way to control algae. It is a very fast growing plant; it’s growth can only be described as ‘explosive’. This means that it also takes up nutrients at a very fast rate. As Duckweed is a floating plant, it draws nutrients straight from the water column. Some people view this as a negative thing, reasoning that if the Duckweed are taking up the nutrients then the plants are not receiving all the nutrients that they need. However, Duckweed are simple plants and stem plants, being more complex, are able to take up nutrients before the Duckweed can get to them. This means that only excess nutrients are taken up by Duckweed and that algae are not able to utilise those excess nutrients. As Duckweed are floating plants they also limit the amount of light entering the aquarium water. Light plays a major role in algae growth and by limiting it, you reduce the chance of algal blooms.
Negative Aspects of Duckweed
As with almost anything, there is a downside to Duckweed. Once Duckweed does become established in an aquarium, it is almost impossible to completely remove it. Duckweed also has the annoying habit of clinging to everything that it touches, which includes anything that you remove from your aquarium and will cling to yours hands and arms when doing tank maintenance. This is a minor annoyance and can easily be resolved by removing some of the Duckweed.
Another problem with Duckweed, although very rare in aquariums, is that if allowed to completely cover the surface of the water, Duckweed can lead to oxygen deprivation and may cause fish deaths.
Note from Author
The key to keeping Duckweed in the aquarium without problems is control. As long as the Duckweed is controlled, it will cause no problems. Removing Duckweed is very simple and it can easily be removed by moving a net across the surface of the aquarium water. Although there are some negative aspects to Duckweed, much benefit can be gained by keeping it in your aquarium. I would encourage people to use Duckweed to its full advantage and look past what minor annoyance it may cause.