How to Get Rid of Duckweed in an Aquarium

Duckweed is a small floating plant that has unparalleled benefits for both aquarium fish and planted tank:

  • Acts as an extra food source – Duckweed has a high protein content that supplements your homemade and commercial fish food.
  • Improves water quality – Duckweed has a fast nutrient intake of nitrates and phosphates, which are natural fertilizers. It keeps the aquarium water free from toxins buildup.
  • Inhibits algae growth – In addition to absorbing dissolved nutrients, duckweed often covers the entire water surface, limiting sunlight’s reach into the water. This limits the unwanted growth of algae.
  • Create hiding spots – Duckweed increases plant cover which enables fish to hide from predators and also nest their fry.
  • Increases the aquarium’s aesthetic – Duckweed gives your planted tank a natural pond-like appearance.
Duckweed in aquarium

However, despite these advantages, duckweed can quickly turn into a nuisance that needs to be got rid of.

When exposed to proper light, duckweed doubles in number every 16 to 48 hours. You can almost see it spread in your aquarium or pond.

The accelerated growth can kill your aquarium fish and other aquatic plants through suffocation and inhibition of photosynthesis, respectively. 

This is because it not only reduces dissolved oxygen in the water, but it can also cover the water’s surface in less than a week, thus limiting sunlight flow.

To prevent such fatalities, here’s a step-by-step process to manually remove duckweed in your aquarium.

Step 1: Use Hands to Scoop Excessive Duckweed

Getting rid of duckweed using hands is an exhausting but effective method.

Firstly, get a large empty bucket.

Secondly, skim your fingers through the water surface to scoop as much duckweed as possible. Empty the removed duckweed into the large bucket.

Repeat the process until your hands only scoop up little to no duckweed.

Beware that removing duckweed using this method might also get rid of other floating plants you have in your tank.

Step 2: Use a Net to Collect Scattered Duckweed

While using your hands to scoop out the excessive duckweed, some will break away and slip through your fingers.

Skimming a net through the tank will efficiently catch the little bits of duckweed that escaped your hands.

Skim the net through the tanks a few more times until you’re satisfied there’s no duckweed left.

If your aquarium is large and a net is too small, use a skimmer, which is also best for the removal of duckweed in a pond.

However, you don’t have to do this if the goal is only controlling duckweed and you intend to leave some to benefit your aquarium fish and planted tanks.

Step 3: Transfer Your Fish to Temporary Fish Tank

To get rid of duckweed completely, you may need to do a thorough cleaning of the tank.

To do so, move your fish to another tank. If you don’t have other tanks, you can use a clean empty jar or Ziploc bags.

In case you opt for the jar, ensure it hasn’t been washed with any detergents. Soap residue contains harmful chemicals that are lethal to your fish.

fish in a bowl

To help the fish adapt easily to the temporary home, it’s important to maintain the environment they’re used to.

If they’re freshwater fish, scoop some of the fresh water from the tank and pour it in the jar or Ziploc bag. Do the same for saltwater fish.

Also, avoid moving them to a cold room, especially if they’re tropical fish.

Step 4: Clean the Aquarium Equipment and Accessories

In a pond, duckweed will cover rock surfaces and crevices. It’ll hang onto the side of the pond. It’ll also cover the surfaces of other aquatic plants, including floating ones.

It behaves similarly in a tank.

You’ll find duckweed on protruding accessories such as fake aquatic plants, rocks, and driftwood.

You’ll also find it on the filters, tubing, and aquarium glass. 

To allow total duckweed removal and also prevent it from growing again, it’s important to clean all the equipment and accessories it might hide in.

For removable accessories like fake plants and rocks, soak them in boiled water for ten minutes and then rinse them using clean cold water.

To clean the tank’s equipment, use a washcloth to wipe down their surfaces.

Use a net or a skimmer to collect any duckweed debris that falls off.

Step 5: Introduce Duckweed-Eating Fish

It’s impossible to get rid of all duckweed at once. When you’ve removed all the duckweed you can see, it’s time to add fish that eat the water plant.

Different fish species enjoy eating duckweed. They include:

While they view the plant as a food source, they’ll help you in controlling duckweed. 

Some, like goldfish, grass carp, and tilapia, will feed on any growing duckweed before it has a chance of re-establishing itself.

Step 6: Reduce Fish Food

Lowering the amount of food you feed your fish serves two purposes:

  • Motivates the fish to eat duckweed
  • Reduces nutrients in the water

Motivate Fish to Eat Duckweed

Unlike goldfish and carp, most fish such as barbs, bettas, and mollies will only nibble on the duckweed.

Nibbling isn’t enough to control fast-growing duckweed in your tank.

To encourage them to feed mainly on growing duckweed, reduce their amount of food.

Hunger will motivate them to feed on the available duckweed enthusiastically.

Reduce Nutrients in the Water

The more food you give to the fish, the more they’ll defecate.

Also, there’ll be more leftovers.

Decomposing feces and leftovers release nitrates and phosphates into the water. These nutrients are the natural fertilizers that accelerate the growth of duckweed in your tank or pond.

By reducing the amount of food, it means fewer feces and leftovers, thus fewer nutrients.

Scarcity of nutrients will kill any growing duckweed before it establishes itself.

Step 7: Monitor the Tank for Duckweed

At this point, there’s only one thing left to do.

Regularly check the tank for duckweed.

When you find any duckweed that hasn’t been eaten, remove it immediately. Plucking it out as soon as you see it will slow its spread until there’s none left.

Repeating this step will ensure your tank’s free of duckweed in a few weeks.

Alternative Aquatic Plants Instead of Duckweed

Aquatic plants are important for many reasons:

Therefore, even though you’ve got rid of duckweed, you must invest in a few other water plants.

Here’s a list of water plants you can use instead of duckweed:

  • Java ferns
  • Anubias
  • Anacharis
  • Hornwort
  • Java moss
  • Amazon sword
  • Water lettuce
  • Water wisteria

To ensure these plants thrive in tanks, ensure they’re receiving the optimum light intensity.

You can do this by installing a full-spectrum aquarium light and keeping it on for nine to twelve hours a day.

Also, use fertilizers that don’t alter the pH levels of the water to too acidic or alkaline.

The good news about these alternate aquatic plants is that they don’t grow as fast as duckweed.

This means you don’t have to worry about your fish or plants dying due to low oxygen or photosynthesis, respectively.

Ready to Learn More About Taking Care of Your Aquarium?

Whether you’re a skilled aquarist or just getting started, it’s good practice to keep learning about life in your aquarium.

You can join a local or online community of aquarium owners like yourself. In such forums, you’ll find a flow of fresh and innovative ideas you can use to become a better aquarist.

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