Branching Hammer Coral Care Guide (Fimbriaphyllia paraancora)
The branching hammer coral is one of the most rewarding large polyp stony corals you can keep. Large polyp stony coral, usually shortened to LPS, refers to reef-building corals that lay down a hard calcium carbonate skeleton and carry relatively large, fleshy polyps over the top of it. The hammer coral takes its common name from its tentacle tips, which swell into little hammer or anchor shapes that wave gently in the current. Under the blue lighting most reef keepers run, those tips often glow, and a healthy colony in full extension is a centrepiece of any mixed reef.
This guide covers the branching form specifically, Fimbriaphyllia paraancora. Hammer corals come in two skeletal shapes. The wall form (Fimbriaphyllia ancora) grows as a continuous, meandering wall of skeleton, a little like a folded ribbon. The branching form covered here grows as separate heads, each sitting on its own finger of skeleton and joined at the base like a small tree. That difference matters more than it sounds. Separate heads make the branching hammer far easier to propagate, and a little more forgiving, since trouble in one head does not automatically spread across a shared wall of tissue.
You may also see this coral sold under the older name Euphyllia paraancora. For many years all hammers, torches and frogspawn sat in the genus Euphyllia. More recent work has reclassified several of them, including both hammer forms, into the genus Fimbriaphyllia. The two names refer to the same animal and are interchangeable, and you will still see the Euphyllia label used widely in the trade.
1. Species Overview
The branching hammer coral is found across the shallow reefs and lagoons of the Indo-Pacific, where it favours protected areas with gentle, shifting water movement rather than the high-energy reef crest. In the home aquarium it forms a colony of individual heads, each crowned with a mass of tubular tentacles tipped by the distinctive hammer or anchor-shaped ends that give the coral its name.
During the day the polyps inflate and the tentacles extend, hiding the skeleton beneath a shifting cushion of tissue. Unlike some LPS corals that only show their tentacles after dark, the hammer stays extended through the day, which is a large part of its appeal. Base colours run through green, tan, gold and brown, and the tentacle tips are often a contrasting lime green, yellow or cream that fluoresces strongly under actinic and blue lighting.
Because the branching form grows as separate heads on individual branches, a colony gradually builds outward and upward as new heads bud from the base and from existing branches. This growth habit also makes the branching hammer a practical coral to propagate, as we cover below.
2. Difficulty Level and Suitability
We rate the branching hammer coral as intermediate. It is genuinely one of the hardier LPS corals, and of the two hammer forms it is the more forgiving. Damaged or unhappy heads can be dealt with individually without the whole colony being at risk, and it tolerates minor swings in chemistry, light and flow better than many of its relatives.
We still class it as intermediate rather than beginner for one reason: like all Euphyllia, it rewards stability and punishes neglect. A hammer in a mature, stable system is close to bulletproof, but one in a young tank with swinging alkalinity or an untamed nutrient level can decline quickly, and Euphyllia in decline are difficult to turn around. If you have kept a soft coral or two and your parameters hold steady from week to week, you are ready for a branching hammer. If your tank is only a month or two old, let it mature first.
3. Water Parameters
Hammer corals build a calcium carbonate skeleton, so the chemistry that supports that skeleton matters. The figures below are the ranges we recommend for this species. More important than hitting any single number perfectly is holding these values steady, because sudden swings stress the coral far more than a stable reading at the edge of a range.
| Parameter | Recommended range |
|---|---|
| Salinity | 1.025 to 1.026 specific gravity (about 35 ppt) |
| Calcium | 400 to 450 ppm |
| Alkalinity | 8 to 9 dKH |
| Magnesium | 1250 to 1350 ppm |
| Nitrate | 5 to 15 ppm (low but not zero) |
| Phosphate | 0.03 to 0.10 ppm (low but not zero) |
| Temperature | 24 to 27°C |
| pH | 8.1 to 8.4 |
A few of these terms are worth explaining. Specific gravity is a measure of how much salt is dissolved in your water, read against pure water; a value of 1.025 to 1.026 corresponds to natural reef salinity of about 35 parts per thousand. Alkalinity is measured in dKH, or degrees of carbonate hardness, and describes the water’s supply of carbonate and bicarbonate, the raw material corals draw on to build their skeleton. It also buffers pH, which is one more reason its stability matters so much.
Nitrate and phosphate deserve a special mention. These are the nutrients that feed algae, so instinct says to drive them to zero. For a branching hammer that is a mistake: this coral wants its nutrients low but not zero. A tank stripped completely of nitrate and phosphate often produces pale, hungry-looking hammers and can trigger tissue loss, while a tank carrying modest, measurable nutrients tends to grow hammers with fuller tissue and better colour. Aim to keep both within the ranges given: present, but controlled.
4. Lighting Requirements
The branching hammer is a moderate-light coral. Like most reef corals it hosts zooxanthellae, microscopic algae that live inside its tissue and convert light into food through photosynthesis, sharing the sugars with their host. Light is effectively part of the coral’s diet, but the hammer neither needs nor wants the intense lighting that small polyp stony corals or clams demand.
Light on the reef is usually measured as PAR, short for Photosynthetically Active Radiation, which is the portion of light corals can actually use for photosynthesis. Branching hammers do well across a moderate band of roughly 50 to 150 PAR, and many keepers find the sweet spot sits somewhere around 75 to 120. Below that band the coral may stretch and pale as it reaches for light; above it the tissue can look washed out and the polyps may stay tight.
New hammers should always be acclimatised to your lighting gradually, since a coral grown under one system can be shocked by a sudden move into brighter light. Start it lower in the tank, or dim your fixture, then raise the light over a week or two while you watch the polyps. Full, relaxed extension and good colour tell you it is comfortable.
5. Flow Requirements
Flow is one of the details that separates a merely surviving hammer from a spectacular one. The branching hammer wants moderate, indirect water movement, enough to make the tentacles sway gently back and forth in a soft rhythmic motion, but never a direct blast.
Too much flow, especially a direct jet from a powerhead, is a common and easily fixed problem. The tell-tale sign is a coral that deflates and retracts its tentacles back towards the skeleton and refuses to open. Persistent hard flow can also tear the delicate tissue where it meets the skeleton, opening the door to infection. Too little flow is less dramatic but still unhelpful, as detritus settles between the heads and gas exchange suffers.
Aim the output of your pumps so that the current reaches the hammer as glancing, turbulent movement rather than a straight line. Gentle, randomised or pulsing flow suits this coral beautifully.
6. Feeding
Thanks to its zooxanthellae, a branching hammer under appropriate light can meet most of its energy needs from photosynthesis alone, and many colonies grow well with no direct feeding at all. That said, it does respond to feeding, and modest supplemental feeding supports faster growth and fuller tissue.
Hammers are not aggressive feeders in the way some LPS corals are, so keep it simple. Suitable foods include mysis shrimp, small pieces of marine flesh, and prepared coral foods or zooplankton-based blends. A single light feeding a week is plenty. You can spot-feed individual heads with a pipette or turkey baster, or let the tentacles catch food during a broadcast feed. Give newly added corals a few days to settle before you begin feeding them.
Resist the urge to overfeed. Heavy feeding will not make the coral grow proportionally faster, but it will raise nutrients and fuel nuisance algae. Light and regular beats heavy and occasional.
7. Placement and Aggression
This is the most important section to read before you place a branching hammer, because a healthy hammer can quietly kill its neighbours if it is put in the wrong spot.
Like other Euphyllia, the hammer is armed. Its tentacles carry nematocysts, the microscopic stinging capsules that all corals and their relatives use to capture food and defend territory. On top of everyday stinging, the hammer can deploy sweeper tentacles: specialised, greatly elongated tentacles it extends, usually after dark, to reach out and sting anything nearby. These can stretch 15 cm (6 inches) or more beyond the visible outline of the colony, and any coral within reach will be stung, often one-sidedly and severely.
Corals also wage a slower, chemical form of warfare called allelopathy, in which they release compounds into the water that inhibit their competitors. In a well-run tank with good water movement, skimming and regular water changes, allelopathy is usually manageable, but it is another good reason to give a hammer room.
The practical rule is generous spacing. Leave at least 15 to 20 cm (6 to 8 inches) of clear space between a branching hammer and any unrelated coral, and remember to allow for growth, since the colony you place today will be larger next year. There is one welcome exception: hammers are generally peaceful towards their own group, and a branching hammer will usually sit happily alongside other hammers and frogspawn corals, letting you build a striking Euphyllia garden. Torch corals are the exception within the family and tend to be more aggressive, so give them extra separation.
The lower to middle rockwork usually suits the branching hammer best, on a stable shelf with moderate light and indirect flow. Avoid perching it at the very top under the brightest light, avoid sharp rock that the tissue can rub against, and never bury the base in sand.
8. Growth Rate and the Colouration Versus Growth Trade-Off
Under stable conditions a branching hammer grows at a steady, satisfying pace, adding new heads gradually until a single frag becomes a full colony over time. Growth speed depends heavily on stability, above all steady alkalinity, along with good light, appropriate flow and controlled nutrients.
The branching form is an excellent candidate for propagation, one of its great advantages over the wall form. Because each head sits on its own branch of skeleton, a colony can be divided by cutting through the bare skeleton below a healthy head, well clear of the living tissue. Only ever frag strong, established colonies, use clean, sharp tools, and give the new pieces gentle flow and stable water while they heal. Many keepers dip fresh cuts in a coral-safe iodine solution to guard against infection. Because the heads separate so naturally, the branching hammer recovers from this far more readily than the wall form, whose continuous tissue makes clean cutting difficult.
It is worth understanding the trade-off between colour and growth, because the conditions that maximise one do not always maximise the other. In broad terms, brighter light and leaner nutrients tend to intensify colour, as the coral produces more of its own protective pigments and carries fewer of the brownish zooxanthellae. Slightly higher nutrients and more feeding, on the other hand, tend to favour faster tissue growth and new head production, sometimes at the cost of a browner, less vivid look. Neither is right or wrong; it depends on whether you are chasing a fast-growing colony or a show-piece display. Small, deliberate adjustments within the ranges in this guide are how experienced keepers steer their hammers one way or the other.
9. Common Issues and Troubleshooting
Even a hardy coral will tell you when something is wrong, usually by closing up. Learning to read the signs early is the key to keeping a branching hammer for years.
Brown jelly. This is the most serious and fastest-moving problem you can face. It appears as a brown, slimy, jelly-like film of decaying tissue, often starting where the tentacles meet the skeleton, and it can consume a head within a day or two. Act immediately: isolate the affected coral if you can, gently siphon or blow the jelly away, increase indirect flow around it, and consider a coral dip. On a branching colony you have the option of removing an affected head to protect the rest, an advantage the wall form does not offer.
Tissue recession. This is the slow retreat of living tissue off the skeleton, leaving bare white skeleton exposed. It is usually a response to instability or irritation: swinging alkalinity, too much direct flow, a sting from a neighbour, pest damage, or tissue rubbing against rock. Find and fix the cause, then hold conditions rock steady and be patient.
Polyp bailout. Under severe or prolonged stress a hammer may undergo polyp bailout, in which the soft tissue detaches from the skeleton entirely and drifts off as a free polyp in a last-ditch attempt to survive elsewhere. It is an alarming sight and a clear signal that something is badly wrong, usually a serious water quality or stability problem. If you see it, test everything and correct conditions promptly. A bailed polyp can occasionally reattach and survive if it settles somewhere favourable.
Closed or deflated polyps. This is not a disease in itself but the coral’s all-purpose distress signal. Run through the checklist: flow too strong or too direct, light too intense or too weak, a swing in alkalinity or salinity, a stinging neighbour, a nipping fish, or simply a new coral still settling in. Correct the obvious culprits and give it time.
Bleaching or fading. When a hammer loses colour and looks pale or translucent, it has often expelled its zooxanthellae in response to too much light, heat stress or a sharp change in conditions. Ease the light down, confirm your temperature is stable within the range above, and let it recover slowly.
A general principle runs through all of these: stability is almost always the cure. New hammers are best left undipped for the first couple of days after arrival so they can settle, and corals rarely respond well to dramatic intervention. Fix the underlying cause, keep your hands out of the tank, and let the animal recover.
A Note on the Ranges Above
The water parameters and other figures in this guide are a general guideline only. Every reef is different, and the ideal balance depends on your lighting, your other livestock and how you run your system. For a more in-depth, personalised look at what favours colouration versus growth for this species in your particular tank, have a look at our Growth vs Coloration Calculator.
Disclaimer
This guide is provided for general educational purposes only. It is not a substitute for professional veterinary or aquatic health advice, and we cannot guarantee outcomes. Individual corals vary, and the right conditions for your system depend on your lighting, your equipment and the other livestock you keep. If you are unsure about anything, please get in touch with our team before proceeding.