What Is Duckweed?

Duckweed is a free-floating aquatic plant often found in outdoor ponds, lakes, and slow-moving water systems like creeks. These belong to the Araceae family, which includes plants like cala lilies.

This is considered one of the smaller flowering plants in the entire world. An individual duckweed frond only grows up to about 1mm in diameter. Despite its tiny stature, it can double the population in less than two days.

This is a beneficial aquatic plant in the fishkeeping hobby, as it can absorb harmful substances from fish and provide food for fish. But just like any other aquatic plant, if this overgrows, it can be a nuisance to fish and can cause mortality among fish.

Is Duckweed Good For A Fish Aquarium?

Generally, duckweed is considered a good thing for a fish aquarium. But if this is overgrown with control, this can be a good thing, too.

Here are some of the factors that make you grow duckweed in your fish aquarium,

  • Duckweed helps to reduce nutrient levels in water, in turn preventing algal blooms and growths in the tank
  • Duckweed releases oxygen by photosynthesis and acts as an oxygen source for fish.
  • Duckweed can protect the larval and fry stages of fish from predators.
  • Duckweed can also be a food source as some fish enjoy eating duckweed.

There are reasons to grow duckweed in your fish aquarium, which can be problematic if not adequately controlled. Here are some reasons to avoid growing duckweed in your fish aquarium,

  • Duckweed can easily entangle in the filter systems and damage the filter equipment.
  • Overgrowth of duckweed could lead to clocking of sunlight and reduced oxygen levels for fish.

Is Duckweed Killing My Fish?

Overgrown duckweed could kill your fish. Large amounts of duckweed in an aquarium could lead to catastrophic events for your fish.

Duckweed could block sunlight and stop the natural oxygen production within the system. With the natural production of oxygen reduced, if there is no external oxygen supply, fish could die from a lack of oxygen within the tank.

Does Duckweed Help with Ammonia?

Yes. Duckweed helps reduce ammonia levels and clean up your tank.

Like any other aquatic plant, duckweed can absorb ammonia as a nutrient source for its growth. This helps to reduce the ammonia levels in water, giving favorable conditions for fish to live.

Apart from that, duckweed can also absorb nutrients from water. Nitrate is a breakdown product of ammonia, which could adversely affect the aquarium’s water quality. By lowering the nitrate levels in the system, duckweed helps reduce algal growth and maintain a suitable living environment for fish.

The simple fibrous roots in duckweed could also trap macro particles like organic debris and suspended particles within them. This also helps to clean the aquarium environment.

What Are the Disadvantages Of Duckweed?

There are several disadvantages to growing duckweed in your aquarium,  

  • Duckweed could easily overgrow and lead to light blockage. Due to the rapid reproduction of duckweed, these can cover the entire water surface, blocking all the light to the tank. This will eventually lead to lower photosynthesis levels and reduced oxygen levels within the tank.
  • Duckweed could clog the filters and damage the filter systems. Due to their smaller size, they quickly get stuck into the filter systems and trap in sensitive areas of the filter. Sometimes, these can be hard to remove. Accumulation of this duckweed could lead to malfunctioning of filter systems.

Which Fish Eat Duckweed?

  • Goldfish
  • Platies
  • Mollies
  • White Cloud Mountain Minnows
  • Danios
  • Siamese Algae Eaters
  • Bettas

Does Duckweed Oxygenate Water?

Yes, duckweed can oxygenate the water of an aquarium. But these depend on several factors, like the amount of duckweed present, light intensity, and the presence of other aquatic plants.

Even though duckweed oxygenates water by photosynthesis, overgrowth of duckweed could lead to depletion of oxygen levels in the tank system. So, it is better to have control over how you grow duckweed in your aquarium.


As we discussed in this article, duckweed could be a friend to your aquarium and a foe. Growing duckweed might be fine for you if you intend to have every aspect of your aquarium natural. But adding duckweed to your aquarium doesn’t seem as effective if you are adding external filter systems and aerators.


I am Bruce Daniel Holgate from Los Angeles, the founder of aquariumbee.com, environmental scientist and content writer. Researcher and hobbyist in aquarium keeping and fish breeding with 20 years of experience. I'm willing to share my knowledge with you all.