Is Hydnophora rigida suitable for beginners?

It's generally considered an intermediate-level coral, so it's best introduced once you're comfortable with the basics of water quality and lighting management.

Can it be kept alongside other corals?

It can extend sweeper tentacles that irritate nearby colonies, so give it ample distance from other corals. Plan your layout with its eventual branch spread in mind.

What colors does it come in?

Colonies typically show cream or green coloration. Exact shading can vary between individual colonies and tank conditions.

How large does it get?

Branch thickness generally reaches around 7 to 12mm. Overall colony spread varies with tank conditions and time.

Are there any legal restrictions on keeping this coral?

Hydnophora Rigida is listed in CITES Appendix II. International trade requires a permit from the exporting country, but as far as CITES is concerned, no registration is needed to buy or sell individuals already legally in Japan.

Hydnophora Rigida

Hydnophora rigida, sometimes called horn coral, is a reef-building species in the family Merulinidae that grows in clumps of somewhat flattened branches. Its distinctive texture comes from small ridges formed where neighboring polyp walls fuse together, giving the branch surfaces a knobby, wart-like appearance. Colonies typically show cream or green coloration, adding understated texture to a reef layout. This species is generally considered a good fit for intermediate keepers who already have some experience managing water quality and lighting. As colonies fill out, their branching growth habit also invites some thought about tank layout and spacing.

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Hydnophora Rigida key facts

Care level: Intermediate
Size: Branches 7-12 mm thick
Temperature: 24〜26℃
Diet: Mainly nutrition from its zooxanthellae. It extends tentacles at night, so powdered or liquid coral foods offered after lights-out are taken.
Lighting: Give it moderate to strong light. AlgaeBarn puts PAR 101-300 in the moderate band and 301 and above in the high band. Reduce light when the colony is first added and raise it over several weeks.
Flow & Placement: Detritus collects between the branches, so give it moderate to strong randomised flow. It grows fast and burns neighbours with sweeper tentacles, so place it in the middle or upper rockwork with plenty of clearance.
Water Temperature & Quality: Water 24-26C, specific gravity 1.023-1.025 (salinity 33-35 ppt), KH 8-12, calcium 380-440 ppm, magnesium 1300-1400 ppm. Sudden swings in alkalinity are the main cause of tissue loss.
Feeding: Most of its nutrition comes from photosynthesis by its zooxanthellae. Because it extends its tentacles at night, powdered or liquid coral foods offered after lights-out are readily taken.
Notes: It is aggressive and will dissolve any coral within reach of its sweeper tentacles. As a scleractinian it is on CITES Appendix II and international trade requires permits. The IUCN rates it Least Concern.

TraitsStony coralBranchingCITES IIAggressive

About Hydnophora Rigida

Hydnophora rigida (horn coral) is a Merulinidae reef coral with flattened, clumping branches and a knobby texture from fused polyp ridges. It comes in cream or green tones and is generally suited to intermediate-level reef keepers.

7 things to know before welcoming a Hydnophora Rigida

1Give It Room From Neighbors
Hydnophora rigida can extend sweeper tentacles that irritate neighboring corals, so it should be placed with generous spacing from other colonies. When planning your layout, account for how much the branches will spread as the colony grows.
2Provide Moderate-to-Strong Light
Like other reef-building corals, it relies heavily on symbiotic algae for energy, so moderate to fairly strong lighting works well. Sudden increases in light intensity can stress a newly introduced colony, so acclimate it gradually.
3Keep Flow on the Stronger Side
Steady, moderately strong water flow helps keep the branch surfaces clear of debris and supports healthy polyp extension. Areas with sluggish flow tend to accumulate detritus, so choose placement with circulation in mind.
4Watch Polyp Extension
Full polyp extension during the day is one useful sign that a colony is doing well. If polyps stay retracted or you notice tissue recession, treat it as a cue to review water quality and flow conditions.
5Feeding Is Optional
Because most of its nutrition comes from symbiotic algae, target feeding isn't required, though offering fine plankton-type foods occasionally may support growth. Overfeeding can degrade water quality, so keep portions and frequency modest.
6Track Key Water Parameters
As a skeleton-building coral, stable calcium, alkalinity, and magnesium levels matter for long-term health. Regular testing and water changes make it easier to catch drift before it becomes a problem.
7Acclimate With Care
Take time acclimating newly arrived colonies to avoid shocking them with sudden temperature or water chemistry changes. A period of isolated observation before adding it to the main system can also help catch any hitchhiking pests or disease early.

Frequently asked questions about Hydnophora Rigida

Q.Is Hydnophora rigida suitable for beginners?: A.It's generally considered an intermediate-level coral, so it's best introduced once you're comfortable with the basics of water quality and lighting management.
Q.Can it be kept alongside other corals?: A.It can extend sweeper tentacles that irritate nearby colonies, so give it ample distance from other corals. Plan your layout with its eventual branch spread in mind.
Q.What colors does it come in?: A.Colonies typically show cream or green coloration. Exact shading can vary between individual colonies and tank conditions.
Q.How large does it get?: A.Branch thickness generally reaches around 7 to 12mm. Overall colony spread varies with tank conditions and time.
Q.Are there any legal restrictions on keeping this coral?: A.Hydnophora Rigida is listed in CITES Appendix II. International trade requires a permit from the exporting country, but as far as CITES is concerned, no registration is needed to buy or sell individuals already legally in Japan.