Duckweed (Lemnoideae) is the most commonly chosen floating plant within goldfish tanks. Duckweed comes in a variety of sizes, from under a millimetre up to the size of lily pads. It’s easily recognisable, with bright green leaves floating on the surface of the tank.
The plant grows in many parts of the world, including America, the Far East, Europe and the UK.
In its natural environment, it thrives in locations as diverse as marshes and wetlands, rivers, streams, ponds and lakes.
If you’re wondering whether goldfish eat it, the answer is yes. In fact, Duckweed is great for your fish to snack on. It’s nutritious and most goldfish find it to be quite a tasty treat!
Caring for duckweed
Duckweed is a fast-growing plant and can quickly overrun a tank if kept in bright light. This means you may need to prune it now and again to keep it from taking over the tank. If you don’t the plant could block light from reaching other plants and your fish.
You should therefore make sure your tank does not receive more than 12 hours of light per day. More than this can lead to prolific growth, while also encouraging algae.
No supplementary fertilization is required in order for Duckweed to thrive. The plant will gain all the nutrition it needs from the tank water.
Individual specimens will generally live for less than a year, but as the plant reproduces prolifically, duckweed introduced to the goldfish tank will tend to be self-perpetuating for the life of the tank.
Duckweed is fairly delicate, and does not stand up well to being handled manually. Using a net to move and extract duckweed from your tank is the best way to handle it when necessary.
Do goldfish eat Duckweed?
Duckweed can be viewed almost like the “grass" of the tank and, as goldfish are keen grazing fish, they will usually eat their fair share of the plant.
But don’t worry – this helps to provide essential nutrients for your fish and keeps the plant’s growth under control.
Duckweed is a good pick for the goldfish tank as long as it is not allowed to proliferate to cover the entire surface of the tank. Usually, your hungry goldfish will make sure that this doesn’t happen!
Where to buy it
Duckweed can be bought in specialist aquarium retailers, pet shops that sell water plants and even in some garden centers. You can also order it online for delivery through the mail.
It is one of the most inexpensive goldfish tank plants available, usually costing less than $3 per “cup” (small beginner culture). You’ll only need to buy a small quantity, as it will quickly grow to a respectable size on its own.
As duckweed comes in many different guises and can be found all over the world, the best way to select the strain that will suit your tank is to choose one that is native to your home country, fairly small leaved, and readily available for sale.
You should never take duckweed from wild ponds of streams to add to your tank, as you cannot be sure of the water quality or if the plant is carrying any parasitic nasties!