How much light does Halimeda need?

Medium light, around 40–60 µmol·m⁻²·s⁻¹ of PAR. Watts are not comparable between fixtures; PAR is. If the manufacturer does not publish PAR, pick one band lower than the tank depth suggests.

Does Halimeda need CO₂?

No. Marked "not needed": it grows normally in a tank with no CO₂ at all. These are usually slow growers that are also forgiving about light.

What water does Halimeda want?

23–28 °C, pH 8–8.4, 7–12 dGH. At 5 dGH wide it is one of the more forgiving ranges.

How fast does Halimeda grow, and where does it go?

Growth rate: medium. Placement: midground / specimen. Substrate: substrate optional, reaching about 8–20 cm. Difficulty: moderate.

G-02 / 25Marine

Halimeda仙掌藻

Halimeda opuntia · Halimedaceae

A calcified alga whose segments are held up by calcium and alkalinity and which turns into soft white fragments without them.

Illustration to come

G-02 / 25 · Halimeda Halimeda opuntia

SpecificationsPlant atlas

Name: 仙掌藻
Scientific name: Halimeda opuntia
Family: Halimedaceae
Origin: Sandy patches and rubble of Caribbean and Indo-Pacific reefs
Light: Medium light
PAR: 40–60
CO₂: Not needed
Hardness: 7–12 dGH
Growth: Medium
Placement: Midground / Specimen
Substrate: Substrate optional
Height: 8–20 cm
Level: Moderate

Water requirementsMarine

Temp.23–28 °C

pH8–8.4

Salinity1.023–1.026 SG

Alkalinity7–12 dKH

Units: temperature in °C, hardness in German degrees (dGH / dKH), marine salinity as specific gravity at 25 °C, volume in litres. These are the values recorded for the species and do not follow the site unit switcher.

Growing notes

1Every segment is supported by aragonite and needs calcium of 400 to 450 mg/L and 7 to 12 dKH to stand upright.
2Medium light with gentle to medium flow suits it; strong flow snaps the segments and weak flow lets blue-green algae smother them.
3New segments going white, soft and brittle is its clearest sign of missing calcium or alkalinity.
4Broken segments reattach on the sand and grow into new plants, which is how it slowly spreads through a tank.
5Cut at the base when harvesting and the white stem will push new segments; remove the debris so it does not bury corals.

Frequently asked questions

How much light does Halimeda need?: Medium light, around 40–60 µmol·m⁻²·s⁻¹ of PAR. Watts are not comparable between fixtures; PAR is. If the manufacturer does not publish PAR, pick one band lower than the tank depth suggests.
Does Halimeda need CO₂?: No. Marked "not needed": it grows normally in a tank with no CO₂ at all. These are usually slow growers that are also forgiving about light.
What water does Halimeda want?: 23–28 °C, pH 8–8.4, 7–12 dGH. At 5 dGH wide it is one of the more forgiving ranges.
How fast does Halimeda grow, and where does it go?: Growth rate: medium. Placement: midground / specimen. Substrate: substrate optional, reaching about 8–20 cm. Difficulty: moderate.