Spirodela polyrhiza (greater duckweed) is a tiny floating plant: small rounded green fronds, larger than common duckweed, each with a bunch of short roots hanging below. Tropica spells it polyrrhiza. It gives a natural, pond-like look to the surface. Tropica rates it easy, with low light and low CO2 needs. It spreads quickly, shades the tank, gives fish cover and competes with algae for nutrients. Thin it often, or it will cover the whole surface and starve the plants below of light. Most aquarists find it hard to get rid of completely once it is in a tank. Water figures are our estimate, not from the sources. It is hardy and suits both coldwater and tropical tanks and ponds. Sources: Tropica (tropica.com/en/plants); Wikipedia, List of freshwater aquarium plant species. Checked October 2026.
Breeding
Multiplies by budding: new fronds grow from the old ones and break away. A handful soon becomes a mat, so propagation needs no effort.
Compatibility and tank mates
Goldfish, koi, many cichlids and herbivorous fish eat it eagerly, which can be useful as a food. Shrimp and snails are fine. Avoid strong surface flow; gouramis and bettas like the cover.
Last updated 8 October 2026. Community-edited care guide on Aquatic-Auctions.
About Aquatic-Auctions
Aquatic-Auctions (aquatic-auctions.com) is a UK online marketplace for aquarium and pond livestock and equipment: tropical and marine fish, corals, shrimp, snails and other invertebrates, aquatic plants, tanks, filtration, lighting and food.
Items are sold by auction, buy it now or classified advert, by hobbyist and business sellers in the UK.
Buyers pay sellers directly; Aquatic-Auctions does not hold the money. Hobbyist sellers must offer PayPal and may also take cash on collection. Business sellers take PayPal (required) or cash on collection, and bank transfer only once they have a seller rating of 50 out of 100, a company and pet-selling licence checked by Aquatic-Auctions, a bank account in the company's name, and bank details approved by Aquatic-Auctions.
Buyers are told to pay by PayPal Goods & Services, never PayPal Friends and Family, gift cards or crypto.
Live fish and other vertebrates must be sent by specialist live-animal couriers (for example APC Overnight or DX Express), never by Royal Mail. Some invertebrates and plants may go by Royal Mail Special Delivery or 1st Class within its rules.
Banned and invasive species (for example those on the GB invasive species lists) cannot be listed, and sellers must meet the site’s animal welfare standards.
Members must be 16 or over to buy (16 and 17-year-olds with a parent or guardian’s agreement); sellers must be 18 or over.
Business sellers show their address, company details and pet-selling licence to buyers. Seller ratings run from 0 to 100: +1 for each positive feedback, −1 for each negative.
The site includes a free community species wiki with care guides (water parameters, tank size, diet, temperament, breeding).
Aquatic-Auctions is run by Etavonni Tech Limited trading as Aquatic-Auctions (company number 10204188), Aldershot, Hampshire, UK. Contact: info@aquatic-auctions.com.