Duckweed

Overview

Duckweed is the smallest, fastest floating plant in the hobby - a haze of tiny green discs that doubles in days, starving algae of nutrients and shading the tank. It is brilliant at cleaning water and nearly impossible to fully remove once it arrives, so keep it only if you mean to. (Lemna minor.)

Origin & Natural Habitat

Still and slow fresh waters across most of the world.

Appearance

Individual green ovals only a few millimetres across, each with a single tiny root, spreading into a solid green film on the surface.

Why People Grow It - Qualities & Benefits

• Explosive nutrient uptake
• Excellent shade and algae control
• Food for goldfish and some fish
• Costs nothing to start

Care

Light: Any - it thrives from low to high light.

Water: Almost anything within tropical/temperate range.

Substrate: None - floats.

CO₂ & feeding: Not needed.

Placement: Surface (if you want it there permanently).

Extra: ⚠️ Duckweed is famously impossible to eradicate - a single disc stuck to a net, plant or hand restarts it. Think hard before adding it; once in, expect it forever. Skim it, net it, and never move it between tanks you want to keep clean.

Propagation

Divides constantly on its own; the challenge is removal, not growth.

Common Problems & Pests

Takes over the surface and clogs filters; nearly permanent. Skim regularly to keep light reaching plants below.

Toxicity & Safety

Non-toxic and even eaten by goldfish; but a stubborn spreader - dispose dry in the bin and never release outdoors.

Best Suited For

• Heavy nutrient export
• Goldfish and cichlid food
• Anyone who wants it permanently
• NOT for keepers who like a clear surface

FAQ

How do I get rid of duckweed?

With difficulty. Skim it daily, black out the tank, or manually net every disc for weeks - one fragment restarts it. Prevention beats removal.

Is duckweed bad for my tank?

No - it is a superb nutrient sponge and shade plant. The only downside is that it covers the surface and is very hard to remove later.