Duckweed
Lemna minor
Araceae
About
Common duckweed is the smallest flowering plant most aquarists will ever meet: each individual is a flattened green frond a few millimetres across with a single thread-like root trailing beneath it. It multiplies in days, mops up nitrate and ammonia about as fast as anything in the hobby, and hands fry and shy fish instant surface cover. It is also effectively permanent — one frond stuck to a net or a sleeve rebuilds the whole colony — so it should be added deliberately, never by accident.
Care
Scatter it on the surface, keep flow low so it is not dragged under, and skim off roughly a third of the mat each week. No CO2 and no substrate needed, but an untouched mat will shade out the plants below it.
Diet
A pure water-column feeder with a large appetite for nitrogen; dense mats measurably lower nitrate, and skimmed duckweed makes a good green food for goldfish, cichlids and livebearers.
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Frequently asked questions
- What water parameters does a Duckweed need?
- Duckweed does best at 10–30 °C (50–86 °F), pH 5–9 and a general hardness of 2–25 °dGH.
- Where should Duckweed be placed in the aquarium?
- Duckweed works best floating at the surface and reaches around 1 cm.
- Is the Duckweed suitable for beginners?
- Yes — Duckweed is one of the easier species to keep and forgives typical first-tank mistakes, as long as the aquarium is cycled and maintained.