Hornwort
A rootless stem plant that grows extremely fast anywhere, floating or weighted, and strips nitrate out of the water while it does so.
Requirements
- Scientific name
- Ceratophyllum demersum
- Family
- Ceratophyllaceae
- Light
- Low to medium
- CO₂
- Not required
- Nutrients
- moderate
- Growth rate
- Very fast
- Placement
- Background
- Feeding
- water column
- Temperature
- 10–28 °C
- pH
- 6–8.5
- Hardness
- 2–25 °dGH
- Height
- 30–200 cm
Identity
- Common name
- Hornwort
- Scientific name
- Ceratophyllum demersum
- Family
- Ceratophyllaceae
How to plant it
The commonest way to kill an aquarium plant is to install it wrongly. This is the first thing to get right.
Float on the surface
Nutrition reaches this plant mainly through the water column, so liquid fertiliser matters more than substrate nutrition.
Growing conditions
| Input | Requirement | Notes |
|---|---|---|
| Light | Low to medium | Match plants to the light you have rather than raising light to suit the plant — that grows algae. |
| CO₂ | Not required | Not a requirement, though growth is faster with it. |
| Nutrients | moderate | Dose a complete liquid fertiliser. |
| Temperature | 10–28 °C | |
| pH | 6–8.5 | |
| Hardness | 2–25 °dGH | |
| Growth rate | Very fast |
Propagation
Cut anywhere; every fragment grows.
Common problems
- needle drop after transfer
- tangles in filter intakes
- outgrows tank
Work from the observation: melting, yellow leaves, holes in leaves and poor growth.
Fish and invertebrate compatibility
- Resists grazing
- moderate
- Resists digging
- excellent
Worth knowing
- Has no true roots. Planting the base in substrate makes it rot; float it or anchor it loosely.
- Drops its needles dramatically after a change of conditions and then regrows. Expect a mess in week one.
- The best emergency tool for a tank with a nitrate problem, because it grows faster than the algae.
Legal status and responsible disposal
Restriction note
A serious invasive weed in several countries, and prohibited or restricted in some of them. Check the position in your jurisdiction before acquiring. Never dispose of trimmings into a watercourse or garden pond.
Never release aquarium life into the wild
Aquarium animals, plants, and aquarium water must never be released into ponds, rivers, canals, drains or the sea — not even in a country where the species is sold freely. Released fish and invertebrates establish populations that displace native species, and released plants and water carry pathogens, parasites and fragments capable of spreading without any animal at all. If you can no longer keep an animal, rehome it through an aquarium society, a retailer that accepts returns, or another keeper.
Evidence
| Claim | Value | Evidence type | Confidence | Source |
|---|---|---|---|---|
| scientific name | Ceratophyllum demersum | Observed / measured | high confidence | Plants of the World Online |
| temperature | 10–28 °C | Aquarium-literature consensus | high confidence | AquariumHQ husbandry synthesis |
| light requirement | low-to-medium | Aquarium-literature consensus | high confidence | AquariumHQ husbandry synthesis |
| co2 requirement | not-required | Aquarium-literature consensus | high confidence | AquariumHQ husbandry synthesis |
| growth rate | very-fast | Aquarium-literature consensus | high confidence | AquariumHQ husbandry synthesis |
| placement | background | Aquarium-literature consensus | high confidence | AquariumHQ husbandry synthesis |
| ph | 6–8.5 pH | Aquarium-literature consensus | high confidence | AquariumHQ husbandry synthesis |
| general hardness | 2–25 °dGH | Aquarium-literature consensus | high confidence | AquariumHQ husbandry synthesis |
| height | 30–200 cm | Aquarium-literature consensus | high confidence | AquariumHQ husbandry synthesis |
Why we say this
What each figure on this page rests on, and how far that is from being independently established.
Every figure on this page has a provenance. Open any claim to see what AquariumHQ holds for it, which sources say what, and what a claim of that kind actually needs. Different claims need different evidence: an accepted scientific name is settled by one authority, while a legal restriction needs a current primary instrument. A single source is often the right answer rather than a thin one. Light and CO2 categories are aquarium conventions rather than measurements, and are labelled as such — AquariumHQ has taken no PAR readings and does not publish figures it has not taken.
scientific nameOne sourceBased on a verified authoritative source.1 citation, 1 independent origin
Checked against gbif on 2026-08-11 and confirmed accepted.
What this kind of claim needs: accepted botanical name — 1 authoritative source in an appropriate context. Checked against gbif on 2026-08-11. One botanical authority is what this class requires.
What would improve this: Corroborate against a second, independent source.
temperatureAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: how to grow the plant — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Go and read a source. This is reachable and has not been reached.
light requirementAquariumHQ's judgement — no authority publishes thisAquariumHQ's own position, derived from evidenced inputs.
No external authority publishes this. The rationale carries the reasoning.
What this kind of claim needs: how to grow the plant — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Keep the rationale current. There is no source to find.
co2 requirementAquariumHQ's judgement — no authority publishes thisAquariumHQ's own position, derived from evidenced inputs.
No external authority publishes this. The rationale carries the reasoning.
What this kind of claim needs: how to grow the plant — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Keep the rationale current. There is no source to find.
growth rateAquariumHQ's judgement — no authority publishes thisAquariumHQ's own position, derived from evidenced inputs.
No external authority publishes this. The rationale carries the reasoning.
What this kind of claim needs: how to grow the plant — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Keep the rationale current. There is no source to find.
placementAquariumHQ's judgement — no authority publishes thisAquariumHQ's own position, derived from evidenced inputs.
No external authority publishes this. The rationale carries the reasoning.
What this kind of claim needs: how to grow the plant — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Keep the rationale current. There is no source to find.
phAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: how to grow the plant — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Go and read a source. This is reachable and has not been reached.
general hardnessAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: how to grow the plant — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Go and read a source. This is reachable and has not been reached.
heightAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: size a well-kept specimen reaches — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Go and read a source. This is reachable and has not been reached.