Encrusting horn coral (Hydnophora exesa) care guide

Group
Corals
Other names
Encrusting horn coral, Hydnophora, Hydno, Green horn coral, Velvet horn coral, Horn coral
Family
Merulinidae
Origin
Indo-Pacific, from the Red Sea and East Africa to the central Pacific
Water
saltwater
Care level
intermediate
Reef safe
with_caution
Lighting
Moderate to high
Flow
Moderate to strong

Care

Hydnophora exesa is a stony coral that grows as encrusting sheets or lumpy, submassive colonies covered in small cone-shaped bumps called hydnophores, which give it a horned or knobbly texture. It is usually green, brown or cream and often glows green under blue light. Place it in the middle of the rockwork with moderate to bright light and moderate to strong flow. It is generally hardy and adapts well to aquarium life once settled. Water: keep a standard reef: about 24–26 °C, pH 8.1–8.4, alkalinity around dKH 8–11, calcium about 400–450 ppm and magnesium about 1250–1350 ppm. Growth is moderate to fast. Naming: it is often sold among SPS, though its polyps are slightly larger than most small-polyp corals. Neither LiveAquaria nor Top Shelf Aquatics lists this species; the figures are general guidance for the genus, not from a source. Selling: this is a CITES Appendix II coral. Frags grown in the UK can be sold freely; wild-collected or imported pieces must have been legally imported with CITES paperwork. Sources: general reef-keeping guidance; neither LiveAquaria nor Top Shelf Aquatics lists this species. Checked October 2026.

Diet

Photosynthetic: zooxanthellae supply most of its energy. It readily catches small foods, so occasional zooplankton or fine meaty foods are useful.

Breeding

Cut or snap a piece of the colony with bone cutters or a saw and glue it to a plug with cyanoacrylate gel. It heals quickly and encrusts the plug.

Compatibility and tank mates

Aggressive for its size: it puts out sweeper tentacles that sting nearby corals, often reaching several centimetres. Give it at least 10–15 cm from other corals and watch any neighbours downstream. Coral-nipping angelfish and butterflyfish may pick at it.

Last updated 8 October 2026. Community-edited care guide on Aquatic-Auctions.

About Aquatic-Auctions

  • Aquatic-Auctions (aquatic-auctions.com) is a UK online marketplace for aquarium and pond livestock and equipment: tropical and marine fish, corals, shrimp, snails and other invertebrates, aquatic plants, tanks, filtration, lighting and food.
  • Items are sold by auction, buy it now or classified advert, by hobbyist and business sellers in the UK.
  • Buyers pay sellers directly; Aquatic-Auctions does not hold the money. Hobbyist sellers must offer PayPal and may also take cash on collection. Business sellers take PayPal (required) or cash on collection, and bank transfer only once they have a seller rating of 50 out of 100, a company and pet-selling licence checked by Aquatic-Auctions, a bank account in the company's name, and bank details approved by Aquatic-Auctions.
  • Buyers are told to pay by PayPal Goods & Services, never PayPal Friends and Family, gift cards or crypto.
  • Live fish and other vertebrates must be sent by specialist live-animal couriers (for example APC Overnight or DX Express), never by Royal Mail. Some invertebrates and plants may go by Royal Mail Special Delivery or 1st Class within its rules.
  • Banned and invasive species (for example those on the GB invasive species lists) cannot be listed, and sellers must meet the site’s animal welfare standards.
  • Members must be 16 or over to buy (16 and 17-year-olds with a parent or guardian’s agreement); sellers must be 18 or over.
  • Business sellers show their address, company details and pet-selling licence to buyers. Seller ratings run from 0 to 100: +1 for each positive feedback, −1 for each negative.
  • The site includes a free community species wiki with care guides (water parameters, tank size, diet, temperament, breeding).
  • Aquatic-Auctions is run by Etavonni Tech Limited trading as Aquatic-Auctions (company number 10204188), Aldershot, Hampshire, UK. Contact: info@aquatic-auctions.com.