Aquatic PlantsBeginner🌑 Low light
Marimo moss ball
Aegagropila linnaei · also called Marimo, Moss ball, Lake ball, Cladophora ball, Cladophora aegagropila
Generally non-toxic to cats and dogs.
The Marimo 'moss ball' is not a moss at all but a rare spherical growth form of a filamentous green alga, Aegagropila linnaei, that rolls along lake beds into a velvety green ball. Extremely hardy and slow-growing, it is a beloved low-maintenance ornamental for cool aquariums.
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Quick facts
| Category | Aquatic Plants |
| Family | Pithophoraceae |
| Native origin | Cool lakes of the temperate Northern Hemisphere (notably Japan — Lake Akan — and Iceland, plus parts of northern Europe) |
| Care difficulty | Beginner |
| Light | Low light |
| Pet toxicity | Pet-safe |
Light
Low light is ideal (~10-30 PAR); it is naturally adapted to dim, deep, cool lake bottoms. Avoid intense or direct lighting, which can bleach the ball or promote competing algae. No special high-tech lighting is needed.
Water
Prefers cool water, ~5-24 C (best below ~24 C; warmth above ~25-26 C stresses it and can cause browning/breakdown), pH ~6.0-8.0, soft to hard water. Very low nutrient demand. Periodically roll it gently by hand during water changes to keep its shape and prevent the shaded underside from dying.
Soil & potting
No roots and no attachment — it is a free-living algal ball that simply rests on the substrate or glass bottom. Do not bury it; nothing to tie or glue. Place it where gentle flow or manual turning lets all sides receive light.
Environment — humidity, temperature, placement
No CO2 required (and not particularly responsive to it). Prefers gentle flow, which in nature rolls the balls to maintain their round shape; in the aquarium turn them by hand occasionally. Sits on the foreground/substrate; can also be left to drift. Strictly an aquatic (submersed) alga.
Propagation
Propagates by division — gently split a large ball and re-roll each piece by hand (a thread can help hold the shape until it re-forms). Loose filaments can also be gathered and rolled into new balls. Growth is very slow (only a few mm per year).
Toxicity detail
Non-toxic and safe for fish and most invertebrates. IMPORTANT: in its natural lakes (e.g. Japan, Iceland) Aegagropila linnaei is rare, protected and declining, so only buy cultivated stock and never harvest wild balls. Also note that commercial moss balls have been a documented vector for the invasive zebra mussel — inspect/quarantine or buy from reputable, decontaminated sources, and never release moss balls or tank water into natural waterways.
Growth stages
How this plant changes through its life — each stage often has its own care, diet and space needs.
Sources
- Aegagropila linnaei (Marimo) — Wikipedia (encyclopedia)
- Invasive zebra mussels found in aquarium moss balls — USFWS guidance (government)