Duckweed is an aquatic plant that anyone can grow. In fact, it is so easy to grow, that it readily takes over ponds and aquariums unless kept in check. Herbivorous fish, like goldfish and koi, find duckweed a tasty snack, and ducks and geese prefer duckweed to most other aquatic plants. Duckweed is a stemless aquatic plant that floats on the surface of water. Duckweed likes water high in nitrogen and phosphate and is ideal for cleaning water that is overloaded with fish and algae. It is used commercially in waste treatment plants to remove nitrates, nitrites, phosphates and ammonia from water. Because it is easy to grow and will happily live in aquariums, duckweed is often used in research on basic plant biology and physiology.
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Things you need
- Pond or aquarium
- Koi, goldfish or carp
- Plastic bucket
- Fish net or plastic scoop
Duckweed can be found in most pet shops that sell fish and fish supplies, and at garden centres selling aquatic plants. Choose a variety that is hardy in your area.
Choose a pond in full sun with slow moving or still water, that already contains fish, preferable koi, goldfish or carp, and other aquatic plants.
To help the duckweed become established, fill a plastic bucket with water from the pond, making sure you do not have fish or snails in the bucket. Float the duckweed in the bucket. You can partially submerge the bucket in the pond, just make sure fish can't enter the bucket.
Add pond water as necessary to keep the bucket at least half full of water. It will take three to seven days for the duckweed to multiply.
When the duckweed has completely blanketed the water in the bucket, use a fish net or plastic scoop to gently transfer most of the duckweed from the bucket to the pond. Leave a few duckweed plants in the bucket to continue to grow and multiple just in case the duckweed in the pond is eaten by fish.
Continue growing duckweed in the bucket and transferring into the pond until you have sufficient duckweed growing in the pond.
Float several duckweed plants on the surface of an aquarium that contains fish or water that has had fish in it. You can leave aeration systems in place.
Place a cover with lights (any type of light will work) on top of the aquarium.
Feed your fish as normal. In three to seven days the duckweed will begin to cover the surface of the water.
Tips and warnings
- Koi, goldfish, carp, ducks and geese love to eat duckweed and can be added to ponds where duckweed is a problem.
- Duckweed is an excellent supplemental food for koi and goldfish and can improve their health.
- Duckweed will smother algae, and absorb nitrogen and phosphates, turning green water clear.
- Duckweed is very fragile and should be handled gently.
- Thoroughly clean fish nets that have been used in aquariums that contain duckweed to avoid spreading duckweed into aquariums where you don't want it.
- Duckweed multiplies and spreads quickly, never use it in ponds that may overflow into natural waterways.
- Be aware, before adding duckweed to a pond, that it may multiply to such an extent that it can smother other aquatic plants.
- Duckweed will overwinter in ponds, however, you should not allow the pond surface to freeze completely as this may kill duckweed.
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