Azolla pinnata (Blue-Green Water Fern)
A tiny, fast-growing floating fern — a tangle of feather-like fronds that creeps across the surface, green in soft light and a striking red-bronze under bright skies. An Australian native and one of the most useful plants in the aquarium.
Quick Facts
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Scientific name: Azolla pinnata
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Common name: Blue-green water fern / mosquito fern
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Growth form: Free-floating surface fern
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Frond size: Mat typically 1–2 cm deep, individual plants a few mm across
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Growth rate: Very fast — can double in days with nutrients and light
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Lighting: Medium to high (bright light brings out red colour)
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CO2: Not required
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Difficulty: Easy
Is this for you?
Perfect if: you want natural surface cover that pulls nutrients from the water, shades algae, and gives fry and shrimp somewhere to hide — with zero planting effort.
Consider something else if: you need an open water column display; a floating mat blocks light below and must be thinned regularly.
Why choose Azolla?
Azolla partners with a nitrogen-fixing cyanobacterium living inside its fronds, so it feeds on the nutrients your fish produce and thrives even in lean water. Rice farmers have grown it as natural fertiliser for centuries — in the aquarium it works as a nutrient export engine, a fry hideout and a live-food nursery all at once.
Key Benefits
- Absorbs nitrates and phosphates, helping keep water clear and algae down
- Dense roots dangle into the water column — perfect grazing cover for fry, shrimps and daphnia
- Green to red-bronze colour change makes it a genuinely attractive surface plant
- Can be grown outdoors in a bucket or tub and moved into the tank as needed
- Trained hobbyists dry and crush surplus as an inexpensive live or freeze-dried food supplement
Care & Specifications
Simply place the portion on the water surface. It needs no substrate, no CO2 and no planting. Provide medium to strong light and let it float — it will spread across the surface within one to three weeks. Warm water speeds growth; cool, still water slows it. Keep a good air gap above the mat so gas exchange at the surface is not fully blocked.
What will you receive?
One live starter portion of Azolla pinnata — a handful of fresh fronds that will expand to cover a substantial surface area within weeks under your own light and nutrients. Colour at dispatch varies between green and red-bronze depending on growing conditions.
Acclimation & Introduction
Floating plants acclimate quickly: match temperature by resting the container in the tank for a few minutes, then gently place fronds on the surface with roots dropping into the water. Avoid dumping onto the mat — slide the plants off a wet hand or spoon to prevent bruising.
Ongoing Care
Thin the mat before it covers more than half the surface — removed Azolla can be shared, dried or composted. Keep fronds away from filter intakes and outflow jets, which will pull the small plants into the impeller. If the mat yellows and thins, your tank may be too nutrient-lean — a small dash of fertiliser or more feeding brings it back.
Pairs perfectly with
Shrimp and betta tanks, fry grow-out tubs, guppy and medaka displays (medaka love picking at the roots), and outdoor planted tubs in summer shade.
NTA Insight:
Azolla is the fastest living nitrate filter you can own. Keep a dedicated tub or jar outdoors with a pinch of substrate and it will regenerate into an endless supply — one reason we can offer generous portions at this price.
Before You Buy
This is a true weed-growth plant: it will multiply fast in a healthy, nutrient-rich tank. Make sure you are comfortable harvesting the surplus weekly, and never release aquarium floating plants into creeks, dams or stormwater drains.
FAQ
Will it kill my other plants?
No, but a full surface mat shades the water column below. Keep part of the surface open and your stem plants stay happy.
Why is mine red while the photos show green?
Both are normal — bright light and mild nutrient stress turn Azolla red-bronze; softer light keeps it green. Colour simply shifts with conditions.
Is it really native to Australia?
Yes — Azolla pinnata occurs naturally in still freshwater across northern and eastern Australia.
