Hornwort
Ceratophyllum demersum
Also sold as Coontail
Synonyms Coon tail · Rigid hornwort
Hornwort (Ceratophyllum demersum) is a stem plant for the background and the surface, growing to about 100 cm (39.4 in) at a fast pace. It wants 50–82°F (10–28°C), low light and no CO₂, and counts as an easy plant to keep alive.
At a glance
| Type | Stem plant |
|---|---|
| Light | LowThe least light it survives in, not the light it looks best in. |
| CO₂ | Not neededWhether it survives without added CO₂ — not whether CO₂ would help it grow faster. |
| Difficulty | Easy |
| Temperature | 50–82°F (10–28°C) |
| Max height | 100 cm (39.4 in)Grown submersed, left to mature, never trimmed. |
| Growth rate | Fast |
| Placement | planted in the background and floating |
| pH | 6–8 |
Before it goes in
- Hornwort lives under a plain low-light LED — it does not need a planted-tank lamp to survive.
- It grows without CO₂.
- It can be planted in the substrate and left floating.
- Expect it to melt back a few weeks after planting and regrow from the roots — pulling it out at that point is the mistake.
- In too little light it stretches: long bare stems between leaves instead of a bushy plant.
- At about 100 cm (39.4 in) it belongs behind everything shorter — planted at the front it hides the rest of the scape and shades it.
- Its leaves are medium: Goldfish, Electric Yellow Lab and Colombian Ramshorn Snail will eat it.
Can it grow without CO₂?
Yes. Hornwort does not need CO₂ at all.
How much light does it need?
Low light is enough — and that is the survival line, not the “it looks better” line. Below it, this one stretches instead of spreading.
How big does it get?
About 100 cm (39.4 in) tall when it is mature and untrimmed, growing fast, and it does not root at all.
Why is it melting?
That is normal for this one. It usually drops its existing leaves a few weeks after planting and regrows from the roots — leave it in place and it comes back.
Will my fish eat it?
Its leaves are medium, so some will: Goldfish, Electric Yellow Lab and Colombian Ramshorn Snail.
What it goes with
- Plants that run on the same light and CO₂, so they can share a tank without one of them being the odd one out: Water Sprite, Anubias nana 'Petite', Cryptocoryne wendtii and Frogbit.
- Animals that share its temperature range and will not eat or uproot it: Betta, Cherry Shrimp, Angelfish and Bristlenose Pleco.
Often compared with
| Hornwort | Anacharis | Brazilian Pennywort | |
|---|---|---|---|
| Light | Low | Low | Low |
| CO₂ | Not needed | Not needed | Not needed |
| Max height | 100 cm | 80 cm | 60 cm |
| Difficulty | Easy | Easy | Easy |
More plants
Sources (4) · checked Sep 2026
- Growth in low lightlilyblooms.com
- Meltingplantedpro.com
- Growth in low lightscienceinsights.org
- Meltingtheshrimpfarm.com