Giant Duckweed

Giant Duckweed (Spirodela polyrhiza) is a native North American floating plant and one of the easiest floaters to keep in a medaka tub. Its round fronds carry a reddish-purple underside and, unlike common duckweed, a cluster of fine roots that give fry and shrimp somewhere to hide.

Floating plants shade the water to suppress algae and take up ammonia and nitrate straight from the water column, and duckweeds are among the most effective at it: they take up ammonium first and grow fast, which is what you want from a nutrient sponge. The nutrients only leave your tub when you scoop some plants out, so a quick thinning every week or two is part of the job.

Every live fish order already ships with a free assortment of floating plants. This listing is for adding Giant Duckweed specifically, on its own or with any order.

A quick note, because duckweed has a scary reputation. Much of it belongs to common duckweed (Lemna), the tiny kind that jams into filters and can blanket a pond. Giant Duckweed is a different, native plant with larger fronds, each with a cluster of roots, so in my own tubs it lifts out in sheets with a net or your hand. It still grows fast and can still take over a small tub if you ignore it, so skim it regularly and leave some open water. My guide to its benefits and drawbacks has the details.

You'll receive a generous starter portion of at least 10 plants. Kept in decent light it fills in quickly, so a small starter portion soon covers the surface.

Perfect For

• Nutrient uptake
• Fry cover
• Quick green cover
• Low-effort tubs