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How to Get Rid of Duckweed in a Pond in 6 Steps (Without Harming Fish)

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By Lindsey Stanton

duckweed in pond

Duckweed is a common pond plant that you can usually find in the shallower, undisturbed areas of your pond. It’s not harmful to fish, but it does make your water murky and can clog up filters. If you’re looking for how to get rid of duckweed without harming fish, this post has you covered!

aquarium plant divider

Things to Know About Duckweed

duckweed
Image Credit: Piqsels

Before going to war with your weeds, you should know your opponent. Duckweed is often confused with algae. From afar, they both appear as a green slimy film on a water’s surface. However, each duckweed is an individual plant and its roots aren’t interconnected

Because duckweed is a rooted plant, you can’t just cut it off at the surface of the water and expect it to die. It is, however, treated as an invasive weed in some areas because it proliferates and can cause problems by clogging up ponds used for irrigation.

The 6 Steps to Get Rid of Duckweed in a Pond

1. Inspect the Water

The first step in how to get rid of duckweed is to inspect the water.

You’re looking for a shiny, green surface that seems to be in one spot and doesn’t spread around. These are usually your smaller weed patches, the ones where you don’t have to use too much force to pick up when removing them from the pond. Make a note of the rougher patches that will require more work to clean up.

You can also check your water’s pH levels. Duckweed thrives in slightly acidic water and can appear after a period of higher acidity. This would indicate that you have something to do with your pH if the duckweed has appeared on many parts of the pond, but not all.

NOTE: Don’t use chemicals when checking for pH levels.

dipping pH test strip on pond
Image Credit: Jens Rother, Shutterstock

2. Manual Removal

The most natural way you can remove duckweeds from a pond is by hand, and there are several ways of doing this. Remember those small patches from earlier? Simply grab them and pull them out (old gardening gloves will protect your hands). By the time you’ve pulled one out, three more may have appeared to take their place.

Doing this regularly should reduce overall weed levels over time as the plants slowly die off. You can also use nets or mesh bags to capture duckweed from an entire body of water, but be aware that they’ll probably contain other unwanted material like leaves and grass.

cleaning garden pond
Image Credit: AlexReut, Shutterstock

3. Use a Natural Duckweed Treatment

Once you’ve cleared your pond of superficial debris and small patches of weed, you’ll be left with more prominent areas that will require more work to remove. This is when using a duckweed treatment comes in handy.

You can use several things for this, but what works best is simply introducing a natural plant to eat the algae instead of using chemicals or other treatments that cause problems for fish and plants. Some good options include water hyacinth, elodea (an underwater clover), and lilypads. These all have extensive root systems that allow them to spread out quickly to surround their food source without damaging the rest of your pond.

Unfortunately, these plants won’t kill off the duckweed completely the first go around. You may have to use some duckweed killer, an algaecide that will kill the plant, which mostly defeats the purpose of a natural treatment. But that’s a potential reality you should know.


4. Add Duckweed Eaters to Your Pond

Fish like the grass carp and tilapia are natural predators of duckweed and can be helpful in your efforts to reduce or eliminate it from your pond. Other than fish, you can also use aquatic snails, which will consume the weed right at its source. Marine snails like the apple and mystery snail are some excellent examples to include in your pond’s ecosystem.

tilapia fish_Bishnu Sarangi_Pixabay
Image Credit: Bishnu Sarangi, Pixabay

5. Collect the Excess Duckweed

There are many things you can do with the duckweed you collect. You can compost it, throw it in the trash, or even use it to make a stylish duckweed wreath! The most common method is to feed your fish with the weed as a source of nutrients.


6. Reduce Surface Irrigation and Stay on Top of It

Finally, you can reduce how much surface irrigation you need by using deep-water pipes, which will allow water to distribute through the middle of your pond instead of just at the top. This prevents excessive growth of duckweed throughout its season and other plants that grow during this time, including algae.

Staying on top of little scraps before they get out of hand is an essential part of how to get rid of duckweed for good! Once a year could be enough, depending on the size of your pond.

koi garden pond
Image Credit: Ravi Mohan, Pixabay

Why Should You Remove Duckweed from Your Pond?

If that sounds like a lot of work to you, it may be tempting to skip the process entirely. There are a few good reasons which may convince you to complete the above steps. For one, duckweed can be an indicator that your pond is not appropriately maintained.

It’s difficult for aquatic plants to survive in water with excessively high levels of ammonia and nitrates, so if those are present in your pond, this could be why you’re having problems with duckweed. These nutrients also encourage vegetation growth all around the pond, including other types of weeds such as lilies, hydrilla, and algae.

Duckweed is also considered a nuisance among fish owners because it can clog up aquarium filters and cause water conditions to turn cloudy. Not only is this unsightly, but it also promotes the growth of other bad plant species that are much more difficult to get rid of.

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Conclusion

Duckweed is one of those things that’s best handled by knowing why it has grown there in the first place and then taking steps to improve the situation. If your water has turned acidic, then you need to do something about that before the duckweed can grow. Duckweed control can be difficult as they grow quickly. The old saying of ‘an ounce of prevention is worth a pound of cure’ fits here.

Prevention means following proper pond management principles like keeping your water at an optimum pH level, minimizing the use of pesticides and fertilizers in our home gardens near ponds or lakes where runoff could affect them, and making sure we don’t run out of space in our ponds, so plants have to compete for nutrition from our fish tanks.

Related Read: Do Goldfish Eat Duckweed? What You Need to Know!


Featured Image Credit: Andy.LIU, Shutterstock

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