Best Methods to Manage Duckweed in Freshwater Aquariums

Ah, yes—our common nemesis, duckweed.

The bane of many aquarists, yet a fascinating plant in its own right. This floating fern can be both a blessing and a curse.

On one hand, it provides shelter for fry, absorbs excess nutrients, and oxygenates the water.

On the other, it can quickly overtake your tank, blocking light and suffocating other plants.

If you’re keen on adding duckweed to your setup, it’s understandable— duckweed forms a lush green carpet on the surface that makes any tank look gorgeous.

On top of that, it’s hardy and grows without too much fuss. But here’s the rub: it can easily grow out of control.

Manual Removal Methods

When it comes to removing duckweed, there’s nothing more straightforward than doing it manually. While it requires a bit of elbow grease, it’s effective and gives you immediate results.

Netting and Skimming

One of the easiest ways to tackle duckweed is by using a skimmer of fine mesh. It's how we remove most of it here in the shop. We use the little shrimp net available here.

Gently scoop the floating plants from the surface, removing as much as you can. Watch for shrimp or fish fry! Small snails like to cling to the undersides of the plant as well.

For larger tanks, use a bigger net. or better yet: Goldfish!

Some of our stock tanks are large enough to keep a goldfish for just this purpose. They suck up only the tiny annoying duckweed, but leave other floaters undisturbed.

Physical Barriers

Creating a barrier can help keep duckweed confined to one part of your tank. For example, floating rings or a similar device can be used to prevent the spread of duckweed across the entire surface. This makes it easier to manage and reduces the time you spend on removal.

But don’t forget to clean the barriers. Duckweed loves to cling to them.

Manual Cleaning of Aquarium Surfaces

Duckweed clings to everything. Wipe down the glass, décor, and even plant leaves during water changes. A soft sponge or old toothbrush works great for this. It's tedious, but it prevents duckweed from re-establishing itself.

Pay extra attention to corners and around filters where duckweed tends to hide.

Biological Control

Why not let nature do the heavy lifting?

Fish are your first line of defense. There are several species that will readily eat duckweed (some more readily than others!):

• Mollies
• Bettas
• Siamese algae eaters
• Goldfish
• African Cichlids

Snails can be minorly effective. Ramshorn snails love to climb up to the surface and nibble on duckweed. They breed quickly, so you'll have an army of duckweed eaters in no time.

However, biological control has its limits. Fish might get bored of duckweed and move on to yummier food. Snails can overpopulate if not kept in check. And most of the time, duckweed grows faster than your creatures can eat it.

I've found the best approach is to combine biological control with other methods. Just make sure any new additions are compatible with your existing tank inhabitants.

There’s another route you can take, the chemical one. We don't recommend this at all, and only include this option with caution.

Chemical management means basically adding a broad-spectrum herbicide to your water. This is terrible for both you and your fish, and should not be used in a home aquarium at all.

Prevention Tips

Prevention is still your best bet. It's easier to keep duckweed out than to fight it once it's in.

Regular Water Changes

Regular water changes, like 20-30% weekly, is recommended. It removes excess nutrients that duckweed loves. It's also good for your tank overall.

Proper Filtration

Proper filtration makes a big difference. A good filter keeps water moving and makes the water inhospitable to the calm stagnation Duckweed loves.

Balanced Nutrient Levels

Maintaining balanced nutrient levels in your tank is crucial. Avoid overfeeding your fish, as uneaten food decomposes and releases nutrients into the water. Use fertilizers sparingly and only if necessary for other plants.

Limiting Light Exposure

While Duckweed grows rapidly under strong light, ANY light will grow Duckweed. If your aquarium receives a lot of direct sunlight or has intense artificial lighting, consider reducing the light exposure. Simple adjustments, like moving the tank or using a timer for your lights, can help in your fight.

These prevention tips aren't just about duckweed. They're good practices for any healthy aquarium. Stick to them, and you'll have fewer issues overall.