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Duckweed (Lemna minor)

Duckweed is the fastest nutrient exporter in the hobby: a film of pinhead-sized fronds that doubles in days, starving algae and feeding herbivorous fish in the process. Be sure you want it before adding it — eradicating it later is notoriously difficult — and check local regulations before pond use or disposal, as moving it into natural waterways is prohibited in many areas.

Care specifications

TypeFloating
DifficultyEasy
LightLow (20–60 µmol PAR)
CO2Not needed
Fertilizer demandLow
Growth rateFast
Max height1 in
Spread1 in
PlacementFloating
Attaches to hardscapeNo
Snail & shrimp safeYes
Temperature50–85 °F
pH6–8
ColorGreen
TrimmingFrequent
StylesBiotope, Jungle

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Duckweed

Duckweed (Lemma Minor)

$5.99 In stock

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Propagation

Each tiny frond buds off daughters continuously — a colony can double in under a week; thin by scooping.

Frequently asked questions

How do I get rid of duckweed once it takes over?

Persistently. Scoop the surface daily with a fine net, run a surface skimmer, and dim the light for a couple of weeks to slow regrowth — every missed frond restarts the colony. Many keepers simply manage it instead, removing 80 percent weekly and treating the harvest as free nitrate removal.

Is duckweed actually good for anything in an aquarium?

Genuinely, yes. It outcompetes algae for nitrogen, shades skittish fish, and is nutritious live food for goldfish and other herbivores. In heavily stocked or hard-to-plant tanks it is one of the cheapest water-quality tools available — the only catch is that it never leaves.

How do I keep duckweed from spreading to my other tanks?

Treat it like a contagion: single fronds hitchhike on nets, plant bunches, shipping bags, and wet hands, and one frond is enough to seed a new colony. Dedicate equipment to the duckweed tank or let nets dry fully between uses, inspect incoming plants closely, and rinse anything shared before it touches another aquarium.

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