Duncan Coral Care Guide for Beginner Reefers

This Duncan coral care guide is created for newbies of the reef-keeping world. I share the best tricks & tips as well as sheer numbers for the most smooth coral experience. You will know much more about Duncan coral after this article.

Basic Information

Scientific name: Duncanopsammia axifugaCommon name: Duncan CoralType of Coral: Hard (LPS)
Average size: Up to 1 inch per polypOptimal Spacing: 2 to 3 inchesСomplexity: Perfect for beginners

Further in the article, I talk about troubleshooting the most frequent problems that you may encounter dealing with Duncan coral. Make sure to read the whole article, as it’s the only source you are going to need before buying or placing your coral into the tank.

Natural habitat and appearance

Even though Duncan corals are aquacultured most of the time, they still can be found in the wild. Normally these species inhabit the coastal waters of Australia and sometimes the Indo-Pacific ocean.

What makes this species stand out among others is its unique shape. No analogs to this coral are found in other geographies. Being somehow similar to a hammer, torch, and frogspawn corals, Duncan coral is a solid hybrid, combining the treats of other species.

However, a whole bunch of colors available is not the case for Duncan corals. If you are after a full-fledged palette, aesthetic and unique appearance (like you can get on hammer or torch corals, for example), maybe Duncan coral is not for you. They pretty much are really green in the center with a whitish cream body and tentacles (which can be purple as well). Some species have cobalt blue, neon green, and variations in between.

The disk-shaped structure refers to the alternative names of the species — branched disc, whisker, and Duncanops coral. They can be classified as large-polyp stony corals, meaning that Duncan corals live within the calciferous tube (made of calcium) Fleshy part can extend over the tube after a solid amount of time when the corals grow big enough. This is why you want to replace them correctly. 

Placement in a Reef Tank

Duncan corals inhabit the warm waters of the pacific ocean and the coastal part of Australia. Those waters boast low to moderate turbidity with an average temperature of about 76 degrees Fahrenheit and medium to high illumination. Summing the above up, I would suggest placing your Duncan coral either in the lower part of the tank or straight in the middle. The sweetest spot is the place out of high water flow with moderate distance from T5, metal halides, or LEDs. Leave yourself no chances to place Duncan coral in the outcropping and peak turbulence areas.

The best thing you can do is to place coral amidst the tank and observe. Make sure to provide enough space though. 2 or 3 inches is a great spacing. Provide good conditions and wait for the coral to respond. The next paragraphs will help you to know what exact parameters Duncan coral requires. 

Water Quality

High-quality water almost 100% guarantees your corals to be safe and sound. Well, maybe that’s a little bit over-enthusiastic but you get the idea. Keeping the water healthy positively affects all the tank. From the smallest animals to the enormous colonies. Poor water, on the other hand, is an evil twin, which can cause bleaching, retracting, and diseases.

Water quality consists of several major factors. Which are calcium, alkalinity, temperature, flow, and pH. Skim to find the one you are not sure about. 


Provide Duncan coral with 400 to 460 ppm calcium levels. Calcium is the major factor that contributes to forming the tube of any large polyp stony (LPS). Start with the recommended minimum of 400 ppm, and level up if needed. You may want to add 10 extra ppm any other week, or even weekly. Take your time and observe other species as well. If they are retracting, or bleaching, make a water change.


Duncan corals prefer medium alkalinity of 450 to 550 ppm with 500ppm being the desired value. Alkalinity is crucial for marine species, so keep it as average as you can. No corals will be damaged if you stick to the average alkalinity. Start from 500 and adjust step by step. The best way to master your knowledge in practice.

Useful info: lots of aquarists prefer 9 to 11 meq\L Alkalinity (the equivalent of 450-550 ppm) Here is a conversion calculator.

pH (power of hydrogen)

Balance is the key in reef-keeping. pH and balance can be used almost interchangeably in the context. pH is the key factor that shows the harmony between alkalinity and acidity in the water. Stick to the 8.1 to 8.4 values to protect your corals and other marine animals. 

Hey, but what if the pH level is higher\lower? 

If pH in your aquarium is higher\lower, make a partial water change immediately. This should help with minerals and pH levels. If that sounds pretty simple for you, consider adding baking soda to raise pH, or vinegar and lemon juice to lower down pH level. You can also consider “pH down” kinds of products to nail down the pH at the desirable mark in the range of 8.1 to 8.4. Never purchase chemicals with muriatic or sulfuric acids in the composition.

Useful tip: Schedule partial water changes (25%) monthly and plan smaller changes of 10-15% every week or fortnight to recover natural pH. 

Temperature and Flow

Duncan coral loves low to medium water flow and a temperature of about 72 to 78 degrees Fahrenheit. Perfect middle values can help you to avoid headaches keeping most of the corals. This is also true-true for Duncan corals. Keep medium turbulence (place corals aside from direct flow peaks) and water warm enough. I encourage you not to overdo the flow or temperature. High turbulence can become one of the tear-the-coral-apart kind of factors, while abnormal temperature disturbs the coral massively (welcome a special guest — Mr.Bleaching, and his company — bacteria, pests, diseases)

Note: it’s normal to lose some heads because of water flow, but with the medium flow, it happens less frequently.


That depends… I’ve encountered any PAR used. My biologist friend suggests as low as 30 PAR. Forum guys swear that they use 200+ PAR and send some photos. Both numbers sound like real ones. Personally, I would stick to the medium of 100 PAR. Metal halides, T5, and LEDs work perfectly. Take your time and observe the coral’s response.

Choosing the spectrum is less flexible. Most corals benefit in a specified range of wavelength which is 400 to 470nm. Tend more to the blue part of the spectrum instead of white. A great ratio to combine both would be 60\40 with the dominance of the blue spectrum. I expose corals for 10 hours with 60% blue and 6 hours with 40% white. Followed by an 8-hour gap. When corals take the rest in total darkness. This combination worked well for me, my friends, and many other aquarists. around the world. Check it out, as the wrong spectrum can lead your coral to bleach, retracting, and even mortality.

Hint: depending on the lightning in the tank, you can get pretty big changes in the coloration of Duncan corals. 

Compatibility with Other Species

Duncan corals feel great in a company with almost all invertebrates. To keep the headache as far as it could be, keep only reef-safe fish. As even perfectly fed unsafe fish can nibble passive corals such as Duncan. Here is a scientific source.

Shortly, you may consider such fish as goby, clownfish, angelfish, tang, mandarinfish, dragonettes, etc.

When it comes to compatibility with other corals, it’s convenient to split them into 3 categories. Aggressors, defensive and passive. Here is the relationship among types:

AggressiveNot compatibleNot compatibleMaybe
DefensiveNot compatibleCompatibleCompatible

Duncan corals are passive, which means they are not a source of any danger. Being a passive type, this species gets along with any other passives, or defensive corals without any problems. However, if you have aggressive corals within the tank, make sure to provide enough space(up to 10 inches in some cases).

The Biggest Problems Related to Hammer Coral 

As you see, the biggest issues are opening and bleaching. Followed by infections and compatibility (which you’ve already read about).

Not opening 

When transferred to a new tank, Duncan may not open up immediately. Give it some time (up to 3 days). If nothing changed, replace it within the tank. Play with lights, water, positioning. Inforce that with a couple of scheduled water changes. If even that didn’t help, the root more likely lies within water parameters. Measure every parameter and adjust to the values I explained above.


The bleaching problem is tightly related to not opening up. As the rule, the reason behind problems is the same — water quality. Check pH, temperature, water flow, and visually evaluate how clean the tank is. Maybe the reason is bacteria. Remember, corals prefer clean water a little bit dirty. It may sound confusing… but don’t over clean the water with carbon.

Tip: partial water changes always help to keep the aquarium mineralized, and pH balanced after cleanings.


Infections occur whether because of external influence (bring new coral to the tank) or because of “evil” bacterias. To avoid two of those, make sure to maintain your filtration system regularly, and dip any coral before placing it into the tank. By simply 5 minute isolation of the newbie, you can save a lot of nerves. Buy a dipping product and immerse any newcomer for 5 to 10 minutes to disinfect it. 

Feeding Hammer Coral

Duncan coral requires no additional feeding. As it lives with symbiont alga which provides up to 90% of the energy used by the coral. 

However, this is a controversial topic. Some hobbyists prefer to feed Duncan coral. They noticed that additional nutrients from food help the coral to grow faster. But still, a major part of the reef-involved people agree upon the fact that feeding is unnecessary turmoil.

If you decide to feed your Duncan coral, I suggest using meaty, or fish food. For example, nauplii larvae, copepods, etc. First, thin the food out in a separate container, then use a turkey baster to pipette the solution over the head of Duncan coral. You should do it carefully, as excessive food leaves a contamination trace (put as little food as possible). Which requires additional cleanings, filtration systems changes. Overall, the results may not be worth your efforts.

You can Install a protein skimmer and filtration system to eliminate the effects of contamination from feeding the corals with food containing protein and amino acids, but that is not 100% protection from bacterias, etc.

How To Frag Hammer Coral

Even though Duncan corals are passive, they still don’t like when you cut them out. Make sure to take safety precautions seriously as toxins can mess up your routine. Goggles and latex gloves are a perfect way to protect both your eyes and arms from toxic excerpts.

To frag hammer coral you can use a bandsaw, or bone shears. Any other method is just fine, as long as you mastered it. The major reason why I use a bandsaw is that it gives back a very clean straight cut (making it easier to glue the cutting onto a frag plug or frag disc later).

First, spot the best place to frag the Duncan coral. Usually, those are the darkest shapes(meaning they are the oldest ones). Once you’ve found the proper place, it’s time to actually make a cut. I use the lower section of my bandsaw to exclude any chances for the coral to release liquids right on my face. 

When the cut is done, I suggest placing the coral into the container water(so it can chill and heal a bit) Also, consider using Iodine disinfectant to help the healing process. Dissolve disinfectant in the water and spread over the stressed area with a pipette or simply blot the surface with a damp, soft towel (soaked in iodine solution). Also, note that I only recommend Iodine if you damaged the coral significantly. (don’t use disinfectant for healthy, untouched coral as it may cause more harm than good).

Then glue the frag to a disc. Spread the glue over the cross-sectional area and give it 5 to 10 minutes to set. I wait about 8 minutes and put the glued frag into the tank. The glue will completely cure under the water. As you see, there is nothing difficult about fragging Duncan coral. Don’t rush and the process will pass with no problem.

In summary, Duncan coral brings back much more than you invest in it. Both in terms of time\result ratio and money. You can grow many heads over a couple of years and sell them to a local marine store almost with no effort. Dedication and just a touch of attention — all you are going to need to keep the Duncan coral in your tank. 

Bart Sprenkels

I have been keeping multiple aquariums since I was 18 years old. Just like many of you, I started with two goldfish but quickly learned they were not suitable for aquariums. Later, I switched to a tropical community tank and I also have two pet musk-turtles in a bigger aquarium. You can read more about me here.

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