9 Pros & Cons Of Having Duckweed In Aquariums

What Is Duckweed?

• Name / Scientific Name: Duckweed / Lemna minor
• Size: 1.5 inches (including root)
• Temperature: 60°-90°F / 15°-32°C
• pH: 6.5-7.5
• Light Requirement: Low
• Toxicity: Not toxic to fish or turtles

Duckweed is a floating aquatic plant that has over 30 different species and is found in slow-moving bodies of water like ponds, lakes, and rivers on almost every continent in the world.

It appears like a green carpet on the water’s surface which can often be mistaken for algae by the untrained eye.

Having duckweed in an aquarium does a great job of removing toxins from the water. It’s super hardy, making it a popular choice amongst newbies and experienced aquarists alike.

Is Duckweed Good For An Aquarium?

Yes, duckweed can be good for your aquarium, but many aquarists avoid it like the plague.

There’s a lot of work involved in keeping it from over-running your tank and it’s super easy to spread it into your other tanks.

As long as you’re prepared for the upkeep, your fish tank can benefit greatly, especially if you have fish that will eat duckweed, more on that further down.

Duckweed is a great option in a turtle tank, turtles love to munch away on this plant, keeping it under control for you.

I’ll go over the pros and cons of duckweed so you can make up your mind if it’s worth the hassle….

Benefits Of Duckweed In Aquarium

First up, the good points.

1. Water Filtration

Like all aquatic plants, duck weed does a great job of removing harmful toxins from the tank water, particularly nitrate, and phosphate.

Fewer toxins = less time cleaning your aquarium and performing water changes, who doesn’t want that?

2. Algae Control

If you have an algae problem and are looking for a solution, duckweed could be the answer.

The main nutrients that algae feed off are nitrate and phosphate, which are the 2 main nutrients that duckweed removes from the water.

Alternatively, you could look at adding some algae eating fish to your tank, if you have algae issues.

Just be sure that your nitrogen cycle can handle the extra bio load of any additional fish that you add to your tank.

3. Water Aeration

Does duckweed oxygenate water?

Yes, it does by removing carbon dioxide from the water and replacing it with oxygen through the process of photosynthesis.

If your water is well oxygenated your fish will be able to breathe properly.

An early warning sign of possibly having low oxygen levels in your water is seeing your fish laying at the bottom of the tank.

4. Food Source

Duckweed makes a good food source as it’s high in fiber and protein and some fish will happily munch away on it.

I’ve left a list of fish that will eat duckweed further down this post.

Most types of turtles will eat duckweed, so it’s a great additional food source for them.

5. Shade & Protection

Fish naturally hide beneath plants and driftwood in the wild, so why not recreate that in their tank?

Breeding tanks can benefit from duckweed as the dense coverage provides the fry somewhere to hide and feel safe while they’re growing.

Because duckweed floats, it will block some light from reaching any other plants you have in the bottom of your tank, so it can be a great option if you find you need to reduce the amount of light in your tank.

Cons Of Duckweed In Aquarium

Now for the cons of duckweed in fish tanks.

1. Nutrient Uptake

Just like the pothos plant, duckweed takes a lot of nutrients from the water, and it doesn’t stop once the excess nutrients have been absorbed.

As duckweed reproduces so quickly, (it can almost double in 2-3 days!) you need to keep on top of keeping it from overrunning your tank, it’s not suitable if you want a low maintenance plant.

If there aren’t enough nutrients in your water to keep all of your plants fed, you could end up with plants dying off and releasing toxins in the water.

Sure the duckweed will absorb a lot of that, but eventually, it will run out of food for itself and will then die off too.

You may then end up with an algae outbreak on your hands as the duckweed breaks down and releases nutrients that algae thrive on.

To prevent this, you can feed your duckweed with a fish-safe liquid fertilizer. I use and recommend Seachem Flourish Nitrogen.

2. Gas Exchange

Carbon dioxide naturally leaves your tank at the water’s surface and oxygen re-enters.

If duckweed completely covers the surface of the water, you’re going to struggle with gas exchange.

Fitting your aquarium with a sponge filter and an air pump should prevent this problem.

3. Equipment Clog

Duckweed gets everywhere. It can easily clog up filter intakes and outlets.

I advise fitting your filter intakes with a pre-filter sponge as a precaution.

4. Shade

Plants that require a lot of light aren’t going to do well with duckweed and will die off releasing toxins into the water.

If you’re wanting to put duckweed in planted aquariums, it’s best to put it with plants that don’t require a lot of light.

Low-light plants that team up great with duckweed include:

• Amazon sword
• Java fern
• Java moss

Where To Buy Duckweed For Aquarium

You can buy duckweed from Amazon or your local garden center, and quite often it will hitchhike in with other live plants you buy.

Is Duckweed Harmful To Fish?

No, duckweed isn’t harmful to fish.

Just make sure you keep its growth under control so it doesn’t cause your other plants to die off, clog your filtration, and stop the gas exchange process.

Will Aquarium Fish Eat Duckweed?

Yes, some aquarium fish will eat duckweed, but there are no guarantees certain types of fish will eat it.

It can be trial and error finding which fish will munch away at it, I’ll list some fish below that give you the best chance of keeping duckweed at bay.

What Fish Eat Duckweed?

Aquarium fish that eat duckweed include:

• Dwarf Gourami
• Electric Blue Acara
• Goldfish
• Lake Malawi Cichlids
• Severum Cichlids
• Tinfoil Barb

How Fast Does Duckweed Grow In Aquarium

Duckweed growth is very fast!

In optimal conditions, the amount of duckweed in your tank can double in just 2-3 days.

As we’ve already established, you must keep on top of its growth by removing it regularly or you could end up having your tank overrun by it in a short space of time.

How To Grow Duckweed In Aquarium

Growing duckweed in an aquarium is easy. In fact, it’s very hard to stop it from growing once it starts.

The only time you will really struggle to grow duckweed is if you have a lot of surface agitation as it likes to grow in still or slow-moving water.

What Does Duckweed Need To Grow

Duckweed needs only 3 things to grow:

1. Still or slow-moving water
2. Light
3. Enough nutrients in the water

Keeping duckweed under control is a whole other matter, but there are some solutions.

How To Control Duckweed In Aquarium

The easiest way to control duckweed in your aquarium is to not put any in your fish tank in the first place, but that can be very difficult as this pesky plant can hitchhike in on other plants unnoticed until it’s too late!!

Many people in the hobby (myself included) avoid it as they feel the cons outweigh the pros.

If you’re still wanting to give it a try, have already added it, or it hitchhiked its way in, you have a few options to help control its growth.

1. Aquarium Ring

The next best way is to keep it contained inside a duckweed aquarium ring.

An aquarium ring is actually designed to keep your fish’s food contained in one place, but it will work fine for keeping duckweed contained too.

2. Increase Surface Agitation

Duckweed reproduces best on the surface of still or slow-flowing water.

Increasing water surface agitation is a great way to control duckweed, this can be done using a powerful HOB filter or having a powerhead at the top of the tank.

Sponge filters can work too, but they tend to only keep the area above the filter free of duckweed.

3. Manual Trimming

Using a net to remove duckweed on a regular basis is the quickest and easiest method to help keep it under control, make sure you don’t use the same net in other tanks unless you want another duckweed outbreak!

4. Limiting The Use Of Tank Lights

Plants use light to grow and reproduce as part of the photosynthesis process.

Limiting the amount of light you give to your duckweed could help with keeping it under control.

5. Keep Fish That Feed On It

As covered further up the post, many fish will eat duckweed, but always make sure your nitrogen cycle can handle the extra bio load before adding new tank mates.

Closing Thoughts…..

So, is duckweed in aquariums good or bad? I prefer not to put it in my aquariums as the cons outweigh the pros for me, but there are many people out there that love duckweed.

If you’re still unsure whether to try duckweed in your aquarium, maybe try similar floating plants that aren’t as high maintenance such as frogbit, water lettuce, or red root floater if you fancy a change from green plants.

Check out the aquascaping section for more guides on making your fish tank look its best.