Marimo ball (Cladophora aegagropila) care guide

Group
Plants
Other names
Aegagropila linnaei (current name), Marimo, Moss ball, Cladophora ball, Lake ball, Japanese moss ball
Family
Pithophoraceae (order Cladophorales, a green alga)
Origin
Cool lakes of the northern hemisphere, including Lake Akan (Japan), Lake Mývatn (Iceland), Lake Zell (Austria) and northern Europe
Water
freshwater
Maximum size
10 cm
Temperature
5–25°C
pH
6.5–8.5
Hardness
5–20 dGH
Care level
beginner
Lighting
Low light; CO2 not needed
Flow
Gentle

Care

The marimo or "moss ball" is not a moss at all but a green alga. Its current name is Aegagropila linnaei; DNA work in 2002 moved it out of Cladophora, so the old name on this page is out of date. In a few shallow, cool lakes, gentle wave action rolls the velvety filaments into spheres with no core; in Lake Akan in Japan they reach 20–30 cm. Wild marimo are protected in Japan and Iceland, and the balls in the trade are farmed elsewhere. Place balls on the substrate in the foreground, or tease them apart and tie the pieces to wood or stone to make a low green carpet. Turn the balls now and then so they keep their round shape and do not go brown underneath. Tropica rates it easy, with low light and CO2 needs. It grows very slowly, about 5 mm a year in the wild. It is adapted to cool water and low light: warm water above about 25 °C and bright light can make it brown or fall apart. Water figures are our estimate, not from the sources. Biosecurity note: in 2021 invasive zebra mussels were found in moss balls sold in North America, which led to recalls. Inspect new balls, and never put old ones or their water into waterways. Sources: Tropica (tropica.com/en/plants); Wikipedia (en.wikipedia.org/wiki/Aegagropilalinnaei); Wikipedia, List of freshwater aquarium plant species. Checked October 2026.

Breeding

Divide a ball into smaller pieces; each piece will slowly round up into a new ball if turned regularly. Pieces tied to wood or stone form a carpet instead.

Compatibility and tank mates

Left alone by most fish; shrimp and snails graze on it without harm. Large cichlids, goldfish and plecos may roll or break the balls. Good for coldwater tanks as well as cooler tropical ones.

Last updated 8 October 2026. Community-edited care guide on Aquatic-Auctions.

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