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Hammer Coral

The hammer coral is one of the most popular large-polyp stony (LPS) corals - a flowing mass of tentacles tipped with hammer- or anchor-shaped heads that sway beautifully in the current.

🗓️ Last reviewed: July 2026

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Overview

The hammer coral is one of the most popular large-polyp stony (LPS) corals - a flowing mass of tentacles tipped with hammer- or anchor-shaped heads that sway beautifully in the current. It is hardy and rewarding, but it packs stinging sweeper tentacles, so it needs elbow room. (Euphyllia ancora.)

Origin & Habitat

Indo-Pacific reefs, on the reef slope in moderate light and gentle-to-moderate flow.

Appearance

Long fleshy tentacles tipped with T- or anchor-shaped ends, in green, gold, or two-tone; the stony skeleton hides beneath the flowing polyps.

Placement & Temperament

⚠️ Aggressive - it extends long stinging 'sweeper' tentacles at night that can kill neighbouring corals. Leave at least 15 cm (6 in) of clear space around it. It generally tolerates other Euphyllia (hammer/frogspawn) but keep torch corals separate.

Tank & Water Conditions

Salinity 1.024-1.026, 24-27°C, stable alkalinity 8-11 dKH, calcium 400-450, magnesium 1300-1350. Stability matters more than perfection.

Lighting & Flow

Moderate light (about 100-175 PAR) and gentle to moderate flow - too much flow and the heads cannot open.

Feeding

Photosynthetic, but responds well to occasional target feeding of small meaty foods, which speeds growth.

Health & Growth

Hardy for an LPS. Watch for 'brown jelly' infection (a fast rotting slime) - isolate and dip an affected head immediately. Never let its skeleton's sharp edges cut you when handling.

Pros & Cons

Pros

Beautiful flowing movement
Hardy, rewarding LPS
Splits into new heads over time

Cons

⚠️ Stinging sweepers - needs space
Brown jelly can spread fast
Sensitive to parameter swings

Hammer Coral - frequently asked questions

How far apart should I place my hammer coral?

Give it at least 15 cm of clear space from non-Euphyllia corals - it fires long stinging sweeper tentacles at night. It usually gets along with other hammers and frogspawn, but keep torches separate.

My hammer looks deflated - why?

Common causes are too much flow, a parameter swing, a nearby coral stinging it, or being pestered by a fish. Check flow and stability first.

🧠 Test yourself: guess the exotic

Three clues from our quiz bank, each about another of our exotic. Can you name them?

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Clue 2.This large, hairy spider can flick irritating hairs from its abdomen as a defense and grows by shedding its entire exoskeleton.

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