Duckweed within the aquarium: profit or nuisance?

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If you have had problems with freshwater algae or maintaining water quality, you may have been recommended a floating plant called duckweed. Aquarium duckweed is generally a small plant that sits on the surface of many lakes and ponds in the wild.

It has been added to the aquarium hobby for both nutrient control and aesthetics. While these plants absorb nutrients very efficiently, their rapid growth rate has often resulted in depleted parameters.

Read on to find out everything you need to know about duckweed care and whether this plant is more of an asset or a nuisance to your freshwater aquarium!


Duckweed is a member of the Araceae family and is a flowering plant, although many species have microscopic flowers; Some species within this family are the smallest flowering plants currently known to science.

Most of the species of duckweed in the hobby belong to the genus Lemna. Because of its ability to absorb nutrients quickly, duckweed has been used as a controlled way to reduce excess nutrients in some waterways. This duckweed is then often harvested and used as fodder and fertilizer.

Scientists are also currently working on extracting certain elements, namely proteins, from modified duckweed in order to make more commercial biomedical advances.

Natural habitat

Duckweed occurs on almost every continent in slowly moving lakes, rivers and pond systems. It usually grows in large mats on the surface of the water that can appear as algae at first if you don't know what you are seeing. It is considered an alien plant in Australia and South America.

While duckweed grow best in full light tropical settings, they have been known to occur in a water temperature range between 5.6 and 33.3 ° C (42 to 92 ° F) with lower light settings. It works best in water with a more neutral pH around 7.0, but it can adapt to more acidic or more basic conditions.

In the wild, duckweed serves as a shelter for many fish, insects, amphibians, and other aquatic species. The large, dense mats also provide a refuge for many larvae and fry to mature. At the same time, the duckweed provides an abundant source of food for many of these species, including birds.


The different types of duckweed can be difficult to tell apart because many of the defining characteristics are microscopic. In the aquarium hobby you are most likely to come across duckweed (Lemna minor).

Common duckweed can have up to four leaves per individual plant. It is common for a 1 to 2 cm (0.4 to 0.8 inch) root to hang in the center of the plant. Each small green leaf is usually rounded or oval and only a few millimeters long and wide. These plants produce flowers on rare occasions, but are too small to see most of the time.

With ideal temperature and water conditions, duckweed populations can double in size overnight. These aquatic plants keep growing until they eventually split up into separate plants. The roots have been optimized for adherence to surfaces, including the legs and feet of birds, to increase populations across aquatic systems.

Is Duckweed Good For Your Aquarium?

So far it seems like duckweed could be nothing but good for aquariums. However, many hobbyists despise duckweed and don't even want them in the same room as their aquarium. Why is this?

Holding duckweed offers many benefits such as nutrient control, protection, shade, and aesthetics. But for such a plant that is so good at it, there seem to be many downsides to actually keeping duckweed in your aquarium, such as nutrient uptake, equipment clogging, and shade.

Benefits of duckweed

Here are some reasons you might want to introduce this tiny plant into your freshwater aquarium.

Nutrient control

The duckweed growth rate is one of the fastest in the hobby. However, in order for these plants to grow, they need many important nutrients such as nitrates and phosphates, which are the main nutrients that often promote algae growth as well.

For this reason, many aquarists add duckweed to their aquarium as a “nitrate sink” in order to outperform the competition from more annoying algae species. The duckweed grows so quickly and absorbs so many nutrients from the water that algae don't get a chance to establish themselves. Duckweed is also recommended for hobbyists who may already be struggling with an algae problem.

However, duckweed need not only be used when algae are present. If you have a water source with unfavorable parameters, this aquatic plant can also help keep nutrients under control and create a more stable system overall.


As in the wild in an aquarium, duckweed can provide protection for fish, invertebrates and amphibians. Some fish naturally stay in areas of the tank with greater coverage. This can be especially useful when the rest of the aquascape is minimal and there aren't many other places to hide.

Duckweed can also be a good addition to breeding or spawning tanks, as fry and other larvae feel particularly safe under the protection of a tight cover.


Duckweed offer protection to your fish and invertebrates, but also protect lower plants from intense lighting. If you're struggling to get the right light distribution for your aquatic plants, these floating plants can be cared for to only cover certain areas of the aquarium, creating shade for less demanding species.

Shade also further helps keep algae from growing in the aquarium by limiting excess light.


In general, floating plants help add more dynamism to the freshwater aquarium. These lush and simple plants can be added to most aquarium systems to add a pop of color or excitement to the top of a tank.

Duckweed also moves with the flow of water surface movement, which can be really fascinating after a while!

Disadvantages of duckweed

Here are some reasons hobbyists keep this plant as far from their aquariums as possible!

Nutrient absorption

While duckweed can be an incredible nutrient export, they don't stop absorbing nutrients once the excess has been removed.

As duckweed absorbs more nutrients, they can reproduce even faster, which ultimately leads to more duckweed plants absorbing even more nutrients! This cycle needs to be precisely regulated if you are to successfully grow other plants in the aquarium, as duckweed can quickly deplete the tank of essential nutrients. To keep nutrients in check, it's best to manually remove duckweed every time they grow a little too quickly.

If you do not monitor the growth rate of your duckweed population, the aquarium can become stripped of all nutrients and then die, which can lead to a surge in ammonia and a subsequent water cycle.

It is also important to note that duckweed, allowed to cover the entire surface of the water, can interrupt gas exchange with the rest of the inhabitants of the tank.

Clog devices

Because duckweed can get out of control so quickly, staying away from their aquarium equipment often becomes a pain for hobbyists. Duckweed likes to get caught in filter inlets and powerheads and can be difficult to get out of. This additional maintenance should be considered when adding duckweed to your aquarium.

In general, it can be very difficult to remove a duckweed colony from the tank at any given point. This aquarium plant is one of those that seems to be coming back no matter how many times you try to get rid of it.


Just as duckweed can be used to shade parts of the aquarium for species with little light needs, it can inadvertently shade areas that may need a lot of light.

Plants need light to photosynthesize and grow. Because duckweed is closer to the light source than most other aquatic plants, the conditions are optimal to outperform most other species. This means that other species with high light needs can easily be prevented from getting the amount of light they need to thrive.

Is duckweed harmful to fish?

It is very unlikely that duckweed will be harmful to fish or other invertebrates unless they get out of hand.

As mentioned earlier, duckweed can quickly cover the top of aquarium and pond systems and shade large parts of the ecosystem. If other plants grow in the area and cannot get enough light and nutrients, these plants can die.

This can lead to mass extinction which can then cause anaerobic conditions due to decomposition and a decrease in total oxygen production in the water column. At this point in time, many organisms would not be able to maintain such low-oxygen conditions.

How fast does duckweed grow in the aquarium?

The duckweed population is known to double overnight. This is not an exaggeration and you should be ready to deal with an ever growing plant.

How do you control duckweed in the aquarium?

Many hobbyists avoid duckweed in their aquariums and ponds at all costs. While this flowering plant can help outperform algae and keep water conditions optimal, the expense of maintaining it usually outweighs the benefits.

Manual removal and surface movement

The best way to combat duckweed is to manually remove some from time to time. For the most part, you'll need to do this every week or every other week. In aquariums, you can use your hand or a net. In a pond, it is best to use a skimmer on a windy day so that all of the plants are pushed aside.

Another way to combat duckweed is to increase the movement of the surface of the water. Most floating plants, including duckweed, do not grow well if they get wet on their leaves because it disrupts gas exchange.

However, with this method, the plants can begin to rot and must be removed immediately. In pond systems, it is best to use an aerator or other fountain mechanism.

Goldfish, koi and other fish

If you have space in your aquarium or pond and have the system set up properly, it may be worth introducing aquarium fish species that use duckweed as a food source. Many pond fish species such as goldfish, carp, koi and tilapia happily eat all available duckweed. Some hobbyists have found that some barbs, mollies, and tetras also eat duckweed, although the chances are they won't touch them at all!

If you don't want your aquarium or pond to be covered with a green mat, you should avoid duckweed entirely. Manual removal is still the best way to get rid of it completely, but it takes time and can get frustrating.


Duckweed is the common name for different types of flowering plants. It is known to absorb nutrients quickly and stabilize aquariums or ponds with algae problems. The rate of growth of duckweed can become unmanageable very quickly, however, and most hobbyists don't want to worry about removing clumps of this plant from their systems later.

If you have any questions about the care of duckweed, how they help aquariums or ponds, or if you already have experience removing duckweed from your own water systems, don't hesitate to leave a comment below!

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