Duckweed in Aquarium: All You Need to Know!

Duckweed is the common name for the simple, tiny, and free-floating flowering plants that scientifically belong to five different genera that include- Lemna, Landoltia, Woffiella, Wolffia and Spirodela, all under the family Lemnaceae.

There are over 30 different species of duckweed. Usually, the leaves and the stem are fused together to form an ovoid flattened shape; and attached root is in the form of fine hairs.

You can buy some Duckweed for your Aquarium on AmazonOpens in a new tab.

They look like an extensive mat while on the surface of water bodies, giving it a lush green appearance. They might also be mistaken for algae sometimes.

Usually, they are transported across by migrating birds, wind, or water current, they can be grown on a large scale, and as well introduced into your aquarium.

However, before introducing them to your aquarium, you have to carefully look at the pros and cons, and this article would be providing you with most of the background information you need.

Where are duckweeds found?

Duckweeds can be found anywhere in the world- Southeast Asia, North America, Africa, Australia, with the exclusion of  Antarctica. However, the prevalence in a particular region is dependent on the particular type of specie.

Those belonging to the genus Lemna are prevalent in Southeast Asia and North America. Those belonging to Wolffia are popular in Australia and Africa and Wolfiella is prevalent in Africa and America.

How to take Care of Duckweed?

An extensive ‘mat’ of duckweed can be very stimulating and beautiful to watch because of their lush green, vivid color. They are very easy to care for. In caring for your duckweed, the major thing to consider is the water conditions of the water body

For duckweeds to thrive, these water conditions have to be met.

Ph: The optimum ph required for their growth is 6.5-7.5. However, they can still survive under a ph of about 9.

Temperature range: They thrive best under temperatures ranging from 68 degrees Fahrenheit to 86 degrees Fahrenheit (or 20 to 30 degrees Celsius). A temperature outside this range would inhibit their growth, and possibly make them dormant.

Light: Adequate exposure to sunlight is the major requirement for photosynthesis to take place, and duckweeds are photosynthetic plants, so they require a good amount of sunlight.

Nutrients: For duckweeds to thrive, a relatively adequate source of NPK (Nitrogen, Phosphorus and Potassium) is required.

Salt content: Because duckweeds are freshwater plants, an increase in the salt content of their habitat might inhibit their growth.

Routine clearing- to avoid overcrowding.

Ensuring a minimal flow of water in the water body. Duckweeds thrive best in slow-moving waters, so an increase in the rate of flow in your water bodies might inhibit their growth.

What are the nutrients contained in duckweed?

Duckweeds have been found to be a nutrient-rich source of food for fishes.

The protein content is about 20-30%, they are believed to be the flowering plants with the highest protein content

  • Fiber: 15-25%
  • Fat: 2-8%

Other nutrients contained include Phosphorus, Potassium, Calcium, Zinc, and sodium.

Which fishes Eat duckweed?

They provide a meal rich in protein for fishes such as Goldfish, Koi fish, Tilapia, Mosquito fish, and Grass Carp.

Apart from being consumed by fishes, duckweeds are consumed in some parts of East Asia and are also a very potent medicinal herb. Also, it can be included in the diet of livestock- including sheep, pigs, and domestic birds.

duckweed aquarium

How Much Sunlight does Duckweed Need?

Sunlight is one of the major requirements for photosynthesis to take place. Photosynthesis is the process by which green plants trap light energy and utilize it in converting carbon dioxide, water and minerals into oxygen and chemicals that are rich in energy.

Duckweeds are photosynthetic plants, so they require an adequate amount of sunlight for them to effectively carry out photosynthesis.

Is duckweed good for an aquarium?

Duckweeds can be very beneficial to your tank, provided that their growth is regulated by routine clearing. A few of the benefits of introducing duckweed to your aquarium include:

A comfortable habitat for aquatic life

The most obvious benefit is the ambiance of nature it gives the water body, the lush green cover makes the water body as natural-looking as possible, mimicking the appearance of wildlife habitat for your fishes to feel comfortable in.

Water filtration

Duckweeds effectively absorb phosphates, nitrates, other chemicals, and even toxins in your tank, thus improving the water quality of your tank by preventing the accumulation of toxic chemicals.

Food source

Since they are low in fiber and rich in protein, duckweeds are also a source of snack for herbivores in your tank to munch on. For some herbivorous fishes, it can be used as their major feed, since it is a rich source of protein.

Control of Algae (and cyanobacteria)

Algae and cyanobacteria require sunlight to thrive and the extensive coverage provided by duckweeds prevents sunlight from entering, thus, limits the amount of sunlight entering the water body, and ultimately resulting in the death of algae and cyanobacteria.

Shade and Protection

The thick mass of duckweed can possibly serve as a shade for your aquarium, helping to reduce the rate of evaporation of water from your tank and maintaining a cool tan environment.

Also, for jumping fishes such as cichlids, the covering provided by duckweed might make it impossible for them to leap out of your tank.

Estimation of water quality in a tank

Duckweeds have short roots that resemble fine hairs. This can give an idea of the water condition in your tank; they thrive best in tanks that are rich in nutrients like nitrates.

If your duckweeds start to develop longer roots, this is an indication that the water condition is quality, since their roots start to lengthen as an adaption method of trying to reach more nutrients, that is, the organic waste in your tank is minimal for them to thrive in. However, this is not a reliable method of measuring the water quality of your tank.

Is duckweed harmful?

As long as their population is minimal, and controlled, they might be very beneficial to your tank or pond. But once there is an overgrowth of duckweed, it becomes dangerous to the ecosystem of the water body because of their sporadic rate of reproduction. This brings us to the question, How is duckweed harmful?

An extensive overgrowth of duckweed covers up the surface of your aquarium, or pond, limiting the amount of sunlight that gets through; thus, they out-compete algae, resulting in the death of some harmful algae, together with other algae which might have been beneficial to your tank as well.

This causes the accumulation of dead algae in your tank, promoting the growth of anaerobic bacteria, and reducing the water quality.

Another way they out-compete algae is by absorbing the excess nutrient in your tank leaving only a few nutrients or the algae to survive on, leading to the death of algae.

Since they are small enough, they can accumulate in your water filter or drains and clog up the filter, reducing the water filtration of your tank; this might result in a reduction in the water quality of your tank.

How fast does duckweed grow?

Duckweeds are one of the fastest growing plants in existence. Some species have been found to replicate in as little as 2 days!

They grow so fast because they have a very effective process of replication which can either be through asexual budding or through sexual reproduction- although their flowers are almost invisible, they are still flowering plants; thus, they are capable of reproducing sexually as well. So, they are equipped with the ability to outgrow other competitors for nutrients.

Another factor that probably makes them grow rapidly is because their system is relatively simple, so energy is not expended in developing complicated stems or roots.

As long as the water is slow-moving and water conditions are optimal, they can double up their mass within 3 days!

How to grow duckweeds?

There are two effective methods of growing duckweed; they can be grown either indoors, or outdoors.

The indoor method involves using duckweed bought from the store or harvesting some from a pond, and then they should be disinfected using potassium permanganate.

Afterward, place them on a tray with enough tap water, ensure that there is no salt in the water (they are freshwater plants, so salt inhibits their growth).

Leave them out in the sunlight for at least 12 hours. You should start noticing an increase in the mass in 5 days.

The outdoor method is more labor-intensive as it requires you to dig a pond if you do not have an established one already.

Add dechlorinator to the water in your pond, and then include your duckweed, which must have been previously disinfected with potassium permanganate into the water, leave in the pond.

You should start to see multiplication in their number in about 5 days.

Regardless of the method used, they have to be controlled by harvesting them routinely, since their growth is aggressively sporadic.

How do you control duckweeds?

Duckweeds are famous for being one of the fastest growing plants. They grow aggressively and can cover up the whole extent of a surface area, irrespective of how large it is; this is as long as the water conditions that support their growth are met.

They are capable of doubling their number in one day.

However, an overgrowth of duckweed can create an unsightly appearance in a water body; in addition to this, it can also deplete the oxygen content in your tank and other harmful effects which we would be discussing in another section.

To prevent this overgrowth and keep your aquarium clean, they have to be properly and constantly controlled. What are the ways to control their sporadic growth then?

Mechanical control

This is probably the easiest method of control. It involves the consistent removal of the duckweeds either manually with your hands, or with the use of a net, rake or any other device that makes it easier for you to scoop out the duckweeds.

As previously mentioned, for this method to be effective, it has to be done consistently, that is, regularly, otherwise, they might keep populating your tank in their large numbers.

A tip to making this method even more effective is to do this on a windy day so that the wind might blow the bulk of the duckweed to one side?

Biological Control

This is another relatively effective method and it involves the use of herbivores, that is, plant-eating animals so that they can consume the duckweeds. Animals that can be used for effective control include Tilapia fish, carp and koi fish.

However, keep in mind that the biological control has to be used before there is a dense overgrowth of these duckweeds because the duckweeds replicate at a rate which might be faster than it can be consumed by these fishes.

Use of an Aeration device

Duckweeds thrive better in stagnant or very slow-moving waters, so you can manipulate this to your advantage by using an aeration device, such as a fountain or the bubble aeration device.

An aeration device increases the oxygen content at the bottom of the water by creating a form of turbulence; this turbulence would inhibit the growth of the duckweeds and cause the death of the duckweeds that are present. This method might be expensive, but it is relatively effective.

Also, there is an added benefit of increasing the oxygen content of your tank and getting rid of any bad odor.

Use of Chemicals

Ideally, this should be the last option. You are advised to use this method only if other methods have been ineffective. Chemicals known as herbicides are used to kill off these duckweeds. These chemicals are diquat bromide, fluridone and are sold under various brand names.

However, you have to be very cautious when using the chemical method of controlling duckweed, because herbicides cause the death of the duckweed and after death, decay follows.

The decomposition can result in the depletion of the water content of the pond or aquarium. Also, chemicals can permeate into the groundwater, which might eventually result in the contamination.

Another thing is that these chemicals might kill off other plants, or might even be toxic for the fishes present in the water tank, so they should be used with the utmost care, while strictly adhering to the instructions on the package.

Limiting sunlight

Another method which might probably be effective is limiting the amount of sunlight that enters the pond, or aquarium; because they are photosynthetic plants, a reduction in the amount of sunlight they receive might inhibit photosynthesis; thus, their growth.

How does duckweed purify water?

Majority of our daily activities constantly result in the contamination of water, and the importance of clear water cannot be overemphasized.

Thus, an efficient system of water purification is required in order to maintain a steady supply of water; and one of the most eco-friendly ways of purifying polluted water is through the use of duckweeds.

In fact, in some developing countries such as India and Bangladesh, they are popularly used in purifying water bodies. This system of purification is more effective in tropical climates.

They are very efficient at absorbing the waste that is produced by the organic life in a water body- this waste might be in form of nitrates, sulfates, and phosphates, which they are particularly efficient at the clearing. They might also absorb other chemicals such as lead,

For water systems that might be polluted by a large number of algae and cyanobacteria, duckweeds can be introduced to suppress their growth and reducing their numbers to a reasonable limit.

Duckweeds outcompete the algae, depriving them of the nutrients and sunlight that they need to grow. However, after using duckweeds to purify a water body, the resulting biomass must be cleared off and adequately disposed of off because they might have absorbed some other metal chemicals such as lead which might be poisonous.

This article has provided in-depth knowledge about the ubiquitous plant that is commonly referred to as Duckweeds. We now know that they are not, in fact, harmful to the organic life in a water body as long as their growth is controlled.

Routine control makes it possible to regulate their growth and this makes them very beneficial for water bodies such as ponds or aquariums.

You can experiment by including a few duckweeds in your aquarium, as far as the tank conditions are optimal, simply ensure that they do not overpopulate your tank.

Saurabh Kumar

I am a passionate fish keeper, with years of experience. You will find some really useful tips and information on this blog about Freshwater Aquariums.

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