Species guide
Marimo Moss Ball Care Guide (Aegagropila)
Aquatic plant
Marimo (Aegagropila linnaei) is a velvety green algae ball — not true moss. It photosynthesizes, rolls in flow, and prefers cool stable water with gentle light. Do not confuse it with Java moss wrapped around a stone or flame/Christmas moss.
- Algae ball
- Not moss
- Cool water
- Roll weekly
Quick facts
| Type | Filamentous algae colony — not bryophyte moss |
|---|---|
| Light | Low; bright LED → brown spots |
| Temp | 18–24 °C ideal; cooler than many tropical tanks |
| CO₂ | Not required |
| Care | Roll weekly; gentle squeeze if fuzzy |
| vs Java moss ball | Java ball is tied moss; marimo is one organism |
| Placement | Midground roll or species-only jar |
| Growth | Very slow — millimeters per year |
Overview
Marimo is not moss. It is Aegagropila, a rolling algae colony. Java moss balls in shops are moss tied around gravel. Flame moss and Christmas moss are bryophytes with attach-and-trim care. Marimo wants rotation, cool water, and patience.
Pair with low-tech scapes: beginner plants · budget nano. Shrimp love it: cherry shrimp. Not a carpet — see Monte Carlo for lawns.
Keep the ball round and green
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Step 1
Roll it weekly
Prevents flat side and dead patch on the bottom. Gentle roll in tank water.
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Step 2
Low light — not a spotlight plant
Marimo browns under strong PAR. Shade or dim LED is fine.
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Step 3
Keep it cooler than a hot discus tank
24 °C max for best color. Warm tanks → slow browning.
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Step 4
Gentle flow, not a powerhead
A ripple rolls it naturally. Stuck in dead corner → mulm coat.
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Step 5
Split only if huge and healthy
Twist apart by hand in bowl water. Both halves need weeks to re-round.
Common problems
Brown or white patches
Why: Too much light or trapped debris on one side.
Fix: Roll; rinse; move to shade; trim bad patch with scissors.
Floats and won't sink
Why: Air trapped inside after squeeze.
Fix: Squeeze underwater until it sinks; don't pierce unless expert.
Falls apart into strings
Why: Old ball, rough handling, or fake/import mix.
Fix: Re-roll loose filaments; buy from reputable source.
Black slime coat
Why: Organic film + low flow.
Fix: Gentle tank-water rinse; improve circulation; shrimp help.
Tank mates
- Cherry shrimp graze the surface — ideal.
- Small fish: neons, chili rasbora — won’t eat a healthy ball.
- Bettas may push it like a toy — OK in 10+ gal.
- Goldfish / plecos: shred or eat it. Skip.
Gear for this species
Landen Aqua Soil Substrate for Natural Planted Aquarium, Plant or Shrimp Stratum, Clay Gravel and Stable Porous Substrate for Freshwater Aquarium, Black Color 40lbs
Substrate vàng chuẩn Iwagumi / Nature Aquarium.
Budget nano under $50 — Marimo is algae — roll it, keep it cool, don't call it moss
FAQ
Is marimo a moss?
No. It is Aegagropila linnaei — a filamentous green algae colony shaped by rolling.
Marimo vs Java moss ball?
Java ball = moss on a core. Marimo = single algae organism. Care differs.
Do I need CO₂ or fertilizer?
No. Low light and stable water are enough.
Why is my marimo floating?
Air inside after cleaning or new purchase. Squeeze underwater.
Can I keep marimo in a betta jar?
Possible short-term with water changes — still needs light roll and stable temp.
How fast does it grow?
Very slow. Expect visible size change over months to years.
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