Moss Ball (Marimo)

The Marimo Moss Ball (Aegagropila linnaei) is not actually a moss but a rare, naturally occurring spherical growth form of a freshwater filamentous algae, native to certain cold, clear lakes in Japan, Iceland, Scotland, and Estonia. In Lake Akan (Japan) they grow as large spheres up to 30 cm in diameter, rolling gently along the lake floor with current and wave action that keeps them round.

In the aquarium hobby, small Marimo balls (3–15 cm) are popular as natural décor items with their velvety, saturated green appearance. They require minimal maintenance — an occasional gentle squeeze to clean debris from the surface, and a slow rotation every few days to ensure uniform light exposure on all sides and prevent flat spots.

Marimo balls grow extremely slowly — approximately 5 mm per year in natural conditions. They can live for decades or even centuries in the right conditions (cool, clean, moderately lit water with gentle movement). They absorb small amounts of nutrients and CO2, contributing marginally to aquarium health.

The balls can be divided if they grow large or begin to turn brown inside (indicating poor light penetration to the core). Tear apart gently, roll the halves into new spheres, and bind temporarily with thread until they maintain their shape.

Light: Low to moderate indirect light (5–20 PAR). They grow best in cool, indirectly lit conditions. Strong direct light causes brown patches and potential algae overgrowth on the surface.

Temperature: Prefers cool water (10–22°C). They can tolerate warmer temperatures (up to 25°C) but struggle above 26°C. In warm tanks, they may turn brown or deteriorate.

Maintenance: Rinse gently in dechlorinated water during water changes. Squeeze gently to remove trapped debris. Rotate regularly for even light exposure. If brown patches develop, increase water changes and indirect light.

No CO2 or Fertilization needed. Marimo are self-contained and don't require supplementation.

Water Parameters: pH 6.0–8.0, temperature 15–25°C, GH 4–20. Prefer clean, clear water with moderate hardness.