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Water Sprite
Ceratopteris thalictroides
Care level: Easy
This fast-growing true fern is found in warm freshwater wetlands across the tropics and subtropics, capable of growing either rooted in substrate or entirely free-floating with its feathery, lace-like fronds trailing in the water. Breeders prize it for the way plantlets sprout directly from the edges of mature leaves, letting a single fern produce dozens of new plants without any deliberate propagation effort.
Adapts to a wide range (~20-50 PAR); grows faster and bushier under higher light but tolerates lower light reasonably well.
Water
Weekly 20-30% water changes; adaptable, pH 6.0-7.5, 22-28°C, soft to moderately hard water.
CO2 & Feeding
Grows without CO2 injection but multiplies faster with it; being a fast grower it benefits from regular liquid fertilizing.
Substrate
Any standard planted substrate works if rooted, though it grows equally well entirely unplanted and floating with roots free in the water column.
Temperature
22-28°C.
Growth speed
Fast
Tank Placement
Midground
Propagation tip
New baby ferns sprout naturally along the margins of older, mature fronds, once a small plantlet has a few leaves and tiny roots, simply detach it and replant or float it elsewhere in the tank.
Care by Season
Spring
Fast growth and plantlet production ramps up; detach and replant baby ferns forming on leaf margins.
Summer
Peak growth, thin regularly whether rooted or floating to prevent it from shading out other plants.
Autumn
Growth slows; fewer plantlets form as light and temperature drop.
Winter
Tolerates cooler water but growth slows considerably; reduce fertilizing to match reduced uptake.
Growing & Maintenance
Planting
Plant it in any standard substrate in the midground, or leave it floating. Rooted plants grow larger and bushier.
Fertilising
Regular liquid fertiliser, as it grows fast.
Trimming
Thin it regularly, whether it is rooted or floating, so that it does not shade out other plants.
Propagation
From the baby ferns that sprout along the edges of older fronds. Detach them once they have a few leaves and roots.
Pests & Diseases
Common problems
Fronds melting after planting
Most likely cause: The plant is adapting to the tank.
What to do: Trim the melted fronds and keep the conditions stable. New fronds follow.
The plant keeps coming loose
Most likely cause: Its fine, hair-like roots anchor weakly, so fish or flow knock it out.
What to do: Replant it more deeply in a calmer spot, or let it float.
Baby plants spreading everywhere
Most likely cause: Plantlets forming on the leaf margins.
What to do: Remove the unwanted plantlets regularly.
Other plants shaded out
Most likely cause: Fast, bushy growth.
What to do: Thin it regularly.
Slow growth
Most likely cause: Cool water.
What to do: Keep the water at 22-28°C and fertilise less while growth is slow.
Pests & Diseases
Melting after planting
Signs: Fronds turn translucent and disintegrate shortly after introduction
Treatment: Trim melted fronds and keep conditions stable; new growth typically appears from the base or crown within weeks.
Uncontrolled spread from plantlets
Signs: Dozens of small ferns appearing throughout the tank
Treatment: Regularly remove unwanted plantlets from leaf margins before they detach and root or float on their own.
FAQ
Should I plant Water Sprite in substrate or let it float?
Both work well, rooted plants tend to grow larger and bushier using substrate nutrients, while floating plants grow faster and provide shade and cover but need more surface space.
Why does my Water Sprite keep uprooting itself?
Its fine, hair-like roots don't anchor as strongly as other plants, so it's often knocked loose by fish or flow; it will happily continue growing as a floating plant if this keeps happening.
Does Water Sprite need CO2?
No. It grows without injected CO2, and multiplies faster with it.
How much light does Water Sprite need?
It adapts to a wide range. It grows faster and bushier under higher light, but tolerates lower light too.
What water does Water Sprite need?
It is adaptable: pH 6.0-7.5, 22-28°C, soft to moderately hard water. Change 20-30% of the water every week.
How do I propagate Water Sprite?
From its plantlets. Baby ferns form on the margins of older fronds and can be detached and replanted, or left to float.
