Marimo moss ball
Aegagropila linnaei
beginner careOverview
The marimo moss ball (Aegagropila linnaei) is the easiest “plant” in the hobby — and technically not a plant or a moss at all, but a rare form of green algae that naturally grows into a soft, velvety sphere. It needs no substrate, no CO2, barely any light, and almost no attention beyond an occasional roll and rinse. It grows incredibly slowly and lives for years, even decades. Cool, quirky and virtually indestructible, it is the perfect first “plant” and a favourite for nano tanks and shrimp setups.
Planting & placement
There is nothing to plant — a marimo simply sits on the substrate or wherever you place it, usually in the foreground where it can be seen. It has no roots. Some keepers let it roll gently in the current, others rest it among hardscape or on a substrate of gravel or sand. It pairs beautifully with shrimp, which graze the debris that collects on its surface. Because it is an algae ball, it does not compete with or shade other plants and fits into any beginner aquascape as a soft green accent.
Light, CO2 & ferts
Marimo wants low to medium light — it evolved in dim, cool lake beds, so strong light can actually harm it and encourages nuisance algae to grow on it. It needs no CO2 and essentially no fertiliser; a normal tank provides everything. It also prefers cooler water than most tropical plants, staying densest and greenest below about 25 °C. In short, the less you do, the happier it usually is.
Propagation & problems
Propagation is as simple as it sounds: split the ball. When a marimo grows large, or if a side browns, gently pull or cut it into smaller pieces and reshape each into a ball by rolling it in your hand — each piece grows on independently. The only real problems are browning where a side is shaded or clogged (fixed by rolling and rinsing) and nuisance algae growing on it under strong light (fixed by dimming the light and rinsing) — see how to get rid of aquarium algae. Give it cool, dim, calm conditions and the odd roll, and a marimo will outlive most of your fish.
Marimo moss ball — frequently asked questions
Is a marimo moss ball actually a plant or moss?
Neither, really — it is a rare form of green algae (Aegagropila linnaei) that naturally grows into a soft velvety ball. It is sold as a plant and cared for like one, but botanically it is an algae, which is why it is so hardy and undemanding.
Why should I roll and rinse my marimo?
Rolling keeps it round and lets all sides get light, so it stays green and dense instead of browning where it sits. Rinsing in old tank water at water changes flushes out trapped debris. Do both regularly and a marimo lasts for years, even decades.
Why is my marimo turning brown or falling apart?
Brown patches mean a side is not getting light or is clogged with debris — roll it, rinse it, and gently squeeze it in old tank water. A ball that flattens or splits can be reshaped by hand, or divided into smaller balls if it has grown large.
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