Hammer Coral Care

Hammer coral is a vibrant addition to any reef tank, and they’re among the most recommended corals for people starting out. Like any coral, however, you’ve got a lot to learn to make sure that they thrive in a tank. You need to know their optimal water conditions, what to feed, and how they interact with other corals as well.

It’s a lot to learn, but we’re here to help. Let’s get to it, and we’ll show you the basic principles needed for excellent hammer coral care.

hammer coral

Hammer Coral Cheat Sheet

  • Classification: Euphylia ancora and Euphyllia paraancora
  • Water Temperature: 74° to 83°F (23° to 28°C)
  • Salinity: 1.024 – 1.026 (32 – 35 ppt)
  • pH: 8.1-8.4
  • Lighting: Low to Medium
  • Flow: Medium
  • Type: Large Polyp Stony
  • Diet: Carnivore
  • Size: 6”
  • Compatibility: High, with exceptions
  • Temperament: Aggressive


The hammer coral gets its name from the shape of the tentacle heads, which are similar to a T or hammer. These coral colonies generally reach around 6” across, although larger specimens are found on occasion.

There are two major varieties of hammer coral to be aware of:

Euphyllia ancora is often known as a “wall hammer” and is less common. This coral grows within “walls” of the skeleton that expand as the coral grows. These are rarer in the hobby since they’re easier to damage when you’re splitting them for propagation.

On the other hand, Euphyllia paraancora is known as a “branching hammer.” These hammer corals have a skeleton that branches into separate nodes for each polyp, which makes them much easier to propagate without causing tissue damage to the coral.

The heads of these hammer corals are a bit different. Euphyllia parancora tends to have a bit more of a U shape to the heads. It’s not a heavily pronounced effect, but it’s noticeable if you’ve seen enough of these corals.

Coloration varies a lot. The dominant color seems to be bright green, with purple also being common. Rare colors include golden, light blue, and even stranger variations. Two-tone corals can also be found.

If you look deeper into the matter you’ll see that some of these colors are shockingly rare, with people often having only seen one or two specimens despite having years in the hobby. Gold and light-blue seem to be the most highly sought after, at least behind rarer specimens and multi-colored corals.

Hammer Coral Tank Conditions

For the most part, Hammer Corals are undemanding in proper reef tank conditions. That’s great news for those who like varied tanks since you don’t have to tailor any parameters specifically for your hammer coral.

Hammer coral come from regions where there isn’t a ton of water movement, just moderate wave activity. This means that they should be placed in a tank with decent flow, but if you allow too much water movement they won’t do well.

The movement of hammer corals is one of the big reasons they’re so popular. Few large polyp stony (LPS) corals allow the polyps to flow in the water. You can monitor the effect of flow on the coral by examining the movement.

As a general rule: your hammer coral should be moving with the current, but it shouldn’t have so much water flowing that the coral ends up “stretched” in one direction. You can, of course, adjust powerheads to make sure flow is optimal in tanks with a little bit more power.

Likewise, lighting is important for these corals. Hammer corals do best in low-to-medium lighting, high lighting can cause issues.

Two nutrients that are particularly important in this case are calcium and magnesium. The latter needs high enough levels to prevent some common problems that occur with hammer corals, the former needs to be over 400ppm for the coral to thrive.

Obviously, the tank will need to be fully cycled before placing the coral into it. Ammonia or nitrite will turn your expensive coral into a pile of brown muck in no time. A mature tank is even better, especially if it’s been stable for over six months.

If you’re new to the hobby, then you’ll find that keeping hammer corals is challenging but not impossible. Like every other part of the aquatic hobby, maintaining water quality is the key to ensuring a long, productive life for your hammer corals.

How to Select a Healthy Specimen

Finding hammer corals is easy enough, finding a healthy one is the main problem for most reef tank keepers. The way frags are created can harm the coral, and hammer corals are prone to bacterial infections. Add in damaged tissue and you have a recipe for disaster.

When examining a coral in the store, you should look for the following:

  • Fully extended polyps
  • No skeleton showing
  • No receding polyps
  • No discoloration or other obvious sign of illness

If you keep the above in mind, then you should be able to bring home a hammer coral that’s likely to live. If not, the coral may be too far gone to survive for the long term even if you plop it right into a tank with perfect parameters.

Try to buy your corals in person, especially if you’ve got a wall hammer coral specimen in mind. It’s much easier to identify health issues while you’ve got the coral in front of you. Online purchasing is convenient, and often ends well, but it’s always better to check the specimen out in person if you’re able.

Selecting a healthy specimen at the outset is a big factor in your success. It’s not always possible to diagnose, and save, a coral before it passes if it was in bad shape initially.

Placement and Defense Mechanisms

Placement of your hammer corals is important to your success. You’ll want to place them in the mid-level of the tank, they don’t do well on the sand or closer to the top.

When placing hammer corals, the more important part of the equation is to ensure that they’re not going to be in active warfare with their neighbors. Hammer coral are very aggressive, and they’ll actively send out sweeper tentacles to destroy nearby corals and keep themselves with adequate living room.

These “tentacles” are closer to the stinging portion of a jellyfish than what most of us think of as tentacles.

There’s varied information on just how dangerous the sweeper tentacles are. Estimates range from, “eh, it’s not too bad” to “can kill other corals off in a couple of hours.” I have a feeling that depends almost entirely on the coral being attacked.

These sweeper tentacles are also capable of affecting humans. If you come into contact with them you may be treated to a nice grouping of welts or blisters, depending on how your body reacts to the venom.

Treatment for stings is pretty standard for marine stuff. Hot water helps break down the proteins faster and hydrocortisone creams can help with any rashes or welts.

I’ve never heard of a case of a severe reaction but if you have any signs of anaphylaxis such as trouble breathing you should seek emergency care immediately. Severe allergic reactions are no joke.

The aggressive nature of these Euphyllia corals doesn’t seem to extend to others in their genus… most of the time. That means they’re usually safe to allow contact with other coral in the same family. There may still be periodic aggression, but it’s usually on a much lower level. Actual tests seem to bear this out, but there are still reports of hammer coral attacking frogspawn or torch coral extensively.

There should be at least six inches of space between hammer coral and any non-Euphyllia corals.

These tentacles can get quite large, reaching up to twelve inches. That said it’s not practical or necessary to space your corals out a foot from each other.

This makes rules for placement pretty easy:

  • Mid-level Placement- The initial colony should be placed on a rock in the middle portion of the tank’s water. Surface or very high placement are both bad ideas.
  • 6” of Breathing Room- Most of these corals will reach a size of about 6” in diameter for the entire colony. Make sure your initial frag has that room to grow into.
  • 6” of Space from Non-Euphyllia Corals- Keep a bit of distance to avoid problematic interactions.

While a complete newbie might misread what their corals are capable of, some common sense and knowledge of their defensive abilities are all you need to make sure that you’ve got a good placement in their tank. 

Common Problems

Hammer corals aren’t prone to any extremely uncommon problems, but you should be aware of the big ones so that you have a chance to save the coral.

Bacterial Infections and Brown Jelly Disease

The biggest threat to a hammer coral is a bacterial infection. It most often results in Brown Jelly Disease which… is pretty much what it says on the box. The coral will begin to develop a layer of brown, gelatinous stuff on its surface.

This is usually accompanied by the coral retracting back into its skeleton as well. A sick hammer coral is hard to miss if you regularly inspect your tank.

This bacterial infection usually comes from tissue damage. It’s common after an improper or careless propagation, but it can also occur from attacks by other animals or anything that might damage the coral.

Brown Jelly Disease isn’t well understood. While it seems to result from a bacterial infection, not every bacterial infection produces the same effect. Tissue samples often show a high level of different microfauna, which appear to be opportunistic rather than the central cause.

In any case, BJD can easily lead to the death of a hammer coral. And it can do so very quickly.

Your best bet is to try dipping it in an antibacterial solution. I’ve seen iodine antiseptic, hydrogen peroxide, and specialized purpose-made treatments all recommended. The important thing is to find the proper dilution.

As a general rule all dips should be based on your tank water. Remove a portion of tank water and mix it with the antiseptic chosen. As a general rule: iodine should be added until the water is almost opaque, while hydrogen peroxide (the standard 2% solution available at the pharmacy) should be added to tank water in a 1:10 ratio.

For ready-made reef medication, follow the instructions on the bottle.

A 10-30 minute period is what’s recommended for a dip, before rinsing the coral gently and placing it back in the tank.

It’s not always possible to save a coral that’s been infected with BJD. If you don’t see improvement soon, or you don’t notice until it’s very late, you may be able to remove the infected pieces of coral. This is much easier with a branching coral, where you can simply remove infected branches, but you can exacerbate the problem even more when you’re dealing with walled hammer corals.


Fortunately, hammer coral isn’t prone to a ton of different parasites. Unlike BJD, this problem is almost always solvable. The ones you do have to worry about have been creatively named Euphyllia Eating Flatworms, or EEFW.

You really don’t want worms chewing on your coral, it’ll kill them over time.

The first line of defense for most aquarists is something like Flatworm Exit that kills flatworms throughout the aquarium. They’re common pests, usually riding in on new corals and in live rock. Follow the directions and be careful, since flatworms are actually toxic to your tank after they’ve died.

The other way to handle things is mechanical removal and dipping. You can even combine the two.

Mechanical removal is usually accomplished with a scalpel. You pull the coral from the tank, place it in a container of tank water, and just pry those little suckers off the base of the coral. If you dipped them first the worms will often be stunned and easier to remove.

You can also use a turkey baster to suck the smaller worms up.

You’ll also need to remove the eggs. This is best done by light brushing with something like a toothbrush, but care needs to be taken to not damage the fragile tissue of the coral.

Regular inspection of the coral, especially the underside of the nodules and the base, is your best defense against serious problems with these worms. They’re remarkably easy to remove from the coral if identified in their early stages.

EEFW can reach up to three inches in length, they’re definitely visible! Inspect corals often, preferably daily, to help keep a problem like this from becoming unmanageable.

Propagating Hammer Corals

Hammer coral propagation is relatively easy if you have a branching specimen.

In that case, you can use either a water-cooled bandsaw or even a pair of bone cutters.

Remove the coral and find a convenient place in the branches to make your cut. You should leave enough room that the flesh of the coral has an inch or so of skeleton left to allow for a decent base to grow.

Some people recommend using saltwater as the coolant when using a bandsaw. I have two thoughts on that.

The first is that it’s a great idea and probably increases the chances of successful propagation.

The second is that it’s going to do an incredible amount of damage to the saw if you don’t carefully clean it after each fragging session.

In any case, you’ll then want to stick the coral in a weak iodine solution for 10-15 minutes before moving the coral back into a suitable tank. The frags are usually glued to a base that keeps them upright and stable before doing so. Any pure cyanoacrylate glue works fine, but unless you’ve got the chemical knowledge to examine ingredients you’ll be better off with a purpose-made glue, such as Reef Glue.

Wall hammer corals are much harder to propagate. Your only choice here is a bandsaw, since bone cutters will leave jagged edges and torn flesh that’s almost a guarantee of infection.

Wall hammers rarely have a convenient place to cut. You’ll almost always have to cut through the flesh of the coral, creating a ton of traumatic tissue damage. A sharp saw, saltwater coolant, and very steady hands will increase your chances of success.

One thing that you need to be aware of is that there’s always the risk of killing a wall hammer coral when you split it. It’s just the way of things. Reef tank techniques move quickly, so if it’s been a while you should look up best practices before any difficult fragging process.

Hammer Coral FAQ

Q: What do I do if my new hammer coral isn’t opening?

A: If it’s only been 1-3 days, you’re most likely in the normal stress range of the coral. They were just pulled up and unceremoniously plopped into a new environment after all! If it’s still closed or mostly retracted after 72 hours, then you may need to change the place within the tank. This is all, of course, if you spent the time selecting a healthy coral with no problems before being brought home!

Q: What do I do if my hammer coral is losing color?

A: Bleaching can occur in tanks with a low pH, incorrect temperature, or just general unhealthy water parameters. Make sure that all of your water parameters are in the right spot and adjust from there. Bleaching is almost always a parameter problem, and not an infection or parasite.

Q: Do I feed a hammer coral?

A: You don’t have to in most circumstances, it just adds more food to the water column and thus more waste. They’ll get the majority of their nutrients through photosynthesis with their symbiotic algae. Feeding seems to have little effect on growth rates overall as well. One exception is when you have an overly aggressive hammer coral, feeding them meaty frozen foods will sometimes cause them to attack less.

Q: How much do hammer coral cost?

A: It depends on the type, size, color, and origin of the coral. Frags can be found from $20 to over $100. For some of the rarer colors (ie: gold hammer corals), you won’t really be able to shop around, they can be hard to find even for those in the wholesale business.

Q: How fast do hammer coral grow?

A: They’re not the quickest growing coral, but they’re not overly slow either. Like many of the other qualities found in a hammer coral… they’re pretty much in the middle. Expect it to take at least 12-18 months for a small frag to become a healthy, thriving coral colony.

Q: How do I check my lighting for a hammer coral?

A: You’ll need to calculate the PAR (photosynthetically active radiation) for corals, rather than just going off of wattage or lumens. You’re aiming for between 75 and 150 PAR, preferably in the 100 range for these corals. Rather than messing around with equations, you can just use a calculator to make sure you’re in the right range.

Q: My previously healthy hammer coral is partially retracted, what’s the cause?

A: In many cases, this turns out to be a magnesium issue. Low magnesium will cause these corals to appear unhealthy, as well as affect other things in your tank, so use your test kit and check it out. 1250 appears to be a good range, and it can make a big difference over even 1100 ppm in the coral’s health.

Stop, Hammer Time!

Hammer corals are beautiful creatures. And with ready availability, they’re a mainstay for those who keep reef tanks. They have modest requirements and tend to be quite hardy while you’re in the right parameters, the main thing to watch out for is their aggressive nature. It’s a small price to pay for keeping these gorgeous creatures in your aquarium. 

So, what’s stopping you from making it hammer time in your reef tank?