Duckweed: Care & Control Guide

Duckweed (Lemna Species) is a small species of floating aquarium plant. They are probably one of the world’s smallest aquarium plants in the world. Duckweed creates a green carpet on the surface of your tank when the surface is quiet and not moving. They make a great plant to remove fish waste from the tank.  

This guide will walk you through all the information you need about duckweed and also how to remove or get them under control.


Duckweed is native to North America, Central America, Asia, Africa, and Europe. They usually grow in ponds and on top of any standing water when water is not toxic. They survive winters in USDA plant zones 4 through 10, this makes them one of the hardy tiny plants on the planet. They have also been introduced into South America and Australia and now they can be found there too. 

Duckweed is a beloved food for ducks which is why it’s named “Duck-Weed” but they are also a favorite food for many other fish and animals. Koi, goldfish, tilapia, carp, poultry, turtles, and many other creatures will joyfully eat duckweed. Duckweed is high in protein and is commercially grown as pet and livestock food in many countries around the world. 

The most common type of Duckweed in the aquarium hobby is “Lemna minor” which has small leaves. This plant is loved by many aquarists as it helps them to remove fish waste from the tank super fast. And at the same time, it’s a hated plant for many aquarists as it grows extremely fast and it’s very hard to get rid of. 



Duckweed is a very tiny plant that measures about 1/16 to 1/8 of an inch in diameter. Plants usually grow up to four leaves before they split and create a new plant. Leaves are flat and oval-shaped with a light green color. 

Duckweeds are flowering species but they rarely produce flowers in an aquarium environment. When they flower, the flower is so tiny that it is super hard to see with the naked eye. 

They have a tiny root structure that is slightly bigger than the leaves. Roots usually have whitish color that can make a great living space for tiny creatures like neocaridina shrimps.

Growth Rate

Duckweed has a super fast growth rate. When they get the right conditions, they will spread very quickly! While this can be a very good thing for fish and other tank inhabitants, their fast growth may cause trouble for you.  

Because they grow rapidly and cover the surface of the tank, they can block the light for any plants that grow below water. They can also deprive tanks of oxygen which can cause health issues for fish and other tank inhabitants. Having a few air bubbles will help you add oxygen back to your tank to help you fight this problem this plant can cause. 

Duckweed Care

Growing and caring for Duckweed in an aquarium is super easy and simple. The only thing you need to know is that this plant can not thrive on moving surfaces. So to make sure your duckweeds thrive and extract all the fish waste from your tank you will have to lower the tank’s surface agitation as much as possible. 

Because this plant covers the surface of the water it will block oxygen exchange in the tank. So to prevent any oxygen shortage in your tank it’s always recommended to have a few air bubbles in your tank. 

Tank Size

Duckweed adapts to any size aquarium; this makes keeping it easy. So you can keep them in a tiny aquarium or a large pond.

Because duckweed is a floating plant, they need more surface to be able to grow and propagate in large numbers. The volume of the water doesn’t affect this plant so it’s always best to pick your tank for other fish and plants and then incorporate duckweed in it. 

Water Conditions

Duckweed needs a stable and still surface of the water to thrive. They also only grow to the amount of nutrition available in the water. 

Apart from that, this plant is super hardy and can grow in almost any water parameter. Below is the ideal range of parameters your duckweed will flourish. 

  • Water temperature: 63° to 79° degrees Fahrenheit
  • pH levels: 6.0 to 8.0 
  • Water hardness: 2 – 15 GH

CO2 Requirement

Duckweed grows on the surface of the water so they don’t need dissolved CO2 (carbon dioxide) in the water. The leaves stay above the water and collect CO2 from the air. 



They need strong light to grow fast. But duckweeds can also tolerate any shade of light from low to high. Simply have the strongest light you can get for your tank and you will soon see a green carpet of plants covering the surface of your tank. When buying light, go for a full spectrum as these lights will give your plants the best chance of growing.


Like most floating plants the duckweed can save you a lot of money when it comes to the substrate. Duckweeds do not require any special substrate as they absorb all the nutrients they need directly from the water.

Duckweed Propagation

Duckweeds can propagate by spreading seeds and by splitting into new daughter plants.

However, duckweeds are most commonly propagated by budding and splitting. 

Each leaf of the plant can become a new independent mother plant and produce more duckweeds. 

Because of their short lifespan, they have evolved to propagate super fast. And the good news is that you don’t have to make anything for them to generate new leaves and plants. 


Maintaining this plant is more about controlling its population than worrying about fertilization or lighting. This plant is hardy and can grow in most aquarium conditions. They are also great at removing fish waste and toxins from your tank. 


With the right conditions, duckweeds do not need fertilization. This plant can survive with a minimum amount of fertilization in the water. Having a few fish in the tank is enough for them to take over the surface of your water. 

Population Control

Because this plant is super small, you will not need to prune or trim them. But because they spread rapidly, they can easily get out of control! 

To keep their population under control, you will need to get them out of your tank every once in a while. When you see duckweeds are overgrown, simply get a fish net and take some of the duckweeds out of your aquarium. 

Remember that is going to be part of your regular maintenance and you need to continuously remove some of the duckweeds to make sure your other plants and fish also experience a better life. 

How to Kill Duckweed.

If you are one of the people that don’t like the hustle of continuously removing duckweeds from your tank then this part of the article is for you.

The most natural way of controlling or completely removing them from your tank is to increase the surface agitation in your tank. Duckweeds can’t survive in the moving waters so creating surface agitation will eventually kill them all. 

Having fewer fish or other aquarium inhabitants will help you lower the amount of nutrition in the water. This can help with lowering their growth rate and keeping their population lower but may not remove them completely. 

Manual removal is another way of getting rid of duckweeds in your tank. But if you miss just a few of them you will get your tanks covered with duckweed in just a few days. 

If you have a larger tank you can add fish like goldfish or koi fish to your tank and they will eat all the duckweed for you. 

Try a combination of these methods for the best and fastest result.

Tank Mates

This plant can also be a great natural light diffuser for fish and invertebrates that prefer to live in shaded areas. They can also create a lot of surface area for your shrimp if you are a shrimp keeper. 

Because this plant lives on the surface of the tank it can live with most fish and invertebrates without any issues. However, there are some exceptions.

If you want your duckweeds to stay in your tank you should avoid adding large herbivore or omnivore fish like koi or goldfish as they will eat duckweeds. Here are our top tank mates for duckweeds:

Is Duckweed Suitable for your Aquarium?

Duckweed is a great plant for removing waste and toxins from the water. Because they are fast growing they will need regular maintenance. 

If you have a tank that has still water then this plant can be a great way to reduce the amount of light that reaches the bottom of the tank. This will help you with controlling algae in your tank. 

However, because other types of aquarium plants also need light, if you have live plants in your tank duckweed might not be an ideal plant to have. Duckweed will block the light on your sensitive plants and might kill them as a result. 

If you have hardy and low-light plants like anubias, then you can safely add duckweed to stop algae growth in your tank. 



By now you can probably tell that duckweed is a super easy aquarium plant that anyone can keep in their tank. Even new aquarium owners can keep them without any issues. Simply get some duckweeds and add them to your tank and enjoy!

Let us know by email or on social media if you have questions. We’re more than happy to help!