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How To Keep Duckweed Out Of Filters – What You Need To Know!

Lindsey Stanton Profile Picture

By Lindsey Stanton

goldfish swimming in tub full of duckweed

Duckweed is generally considered an invasive species when it comes to ponds. Sure, some people like it because some fish like Koi and goldfish eat it, but generally speaking, it is more of a nuisance than anything else. It’s one of the smallest flowering aquatic plants that you can find, and just a few pieces of this stuff can quickly multiply to take over a whole pond.

This can create some pretty big problems when filtration units are concerned. Duckweed can get sucked up into filters, clog them, and even end up shooting out the top, going all over the place. It’s important to know how to keep duckweed out of filters which is what we are focusing on today.

aquarium plant divider

The 3 Methods To Keep Duckweed Out of Filters

1. Use A Pre-Filter

One of the best and easiest things that you can do to keep duckweed out of the filtration unit is to use a pre-filter. A pre-filter is more or less just a mesh bag that you can place over the filter intake which stops larger debris like duckweed from getting sucked in.

It’s pretty much just a type of mechanical filtration that occurs before the water ever really gets into the filter. These things are easy to find, easy to use, and they do not cost that much either.

Other types of pre-filters are more complicated than mesh bags. There are ones that come in the form of PVC tubes filled with sponges or other materials. These let water flow through into the filter without letting large debris like duckweed getting sucked into the filtration intake.

Image Credit: Pixabay

2. Cover The Intake

If you do not want to buy a special pre-filter, you can always create your own with some things that you might have lying around the home1. All you really need is something like pantyhose or some cheesecloth, along with some strong elastics.

Simply place a layer of the fine mesh material, whether the screen from a summer door, pantyhose, or anything else, over the intake, and then use the elastics to keep it there. It really does not get any easier than that.

3. Use A Submerged Filter or Filter Intake

As you probably know, duckweed is a floating plant, one that only grows on the surface of the water. Therefore, if you have a problem with this stuff getting sucked into your filter intake, it is because the filter intake is located on the surface or too close to the surface of the water.

Now, you do not necessarily have to get a submersible filter. However, you should get an intake, or create an intake, that is a good 6 inches below the surface of the water, if not even further down. Since duckweed is not submerged, having the intake far down from the water’s surface should help solve this problem.

fish pond back yard
Image Credit: Lisa Ewing, Shutterstock

divider fish plants 2 The 3 Ways to Get Rid of the Duckweed

Now, some people like having a bit of duckweed in the pond, but if it is such a large problem in terms of clogging your filtration unit, you can always just get rid of it. This might be a little harder than we are making it out to be, as this stuff does multiply fast, and getting rid of all of it at once can be difficult.

However, there are a few options you can go with to get rid of, or at least to reduce the amount of duckweed in your pond.

1. Pond/Pool Skimmer

One simple way to get rid of the duckweed in the pond is to use a pond or pool skimmer. If you have a large pond, you will need waders if you don’t want to get wet. Simply use the skimmer to remove as much of the duckweed from the pond as humanly possible.

big koi pond
Image Credit: Michelle_Raponi, Pixabay

2. Herbicides

There are special herbicides that you can use, ones that trigger weeds like duckweed, but won’t hurt the other plants or your fish. Get yourself some herbicide, make sure that it is non-toxic to fish, follow the directions as stated, and get to work spraying the life out of the duckweed.

You might have to repeat the process a couple of times, but it should work like a charm.

3. Add Duckweed Eaters

The other thing that you can do to cut down on some duckweed is to add duckweed eaters into the pond. Yes, ducks are one option, as are waterfowl, but keep in mind that they will eat smaller fish.

Goldfish and Koi fish love eating duckweed too, so adding a few of those will help cut down on it as well.

beautiful koi fish
Image Credit: IamSuperPear, Shutterstock

aquarium plant divider Conclusion

The bottom line is that keeping duckweed out of your filter is really not all that hard. Between using pre-filters, submerged intakes, and simply getting rid of the duckweed, there are many options that you can go with. We would recommend using a combination of the options we discussed above for the best results.

Featured Image Credit to: Sorakrai Tangnoi, Shutterstock

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