Duncan Coral Not Opening? Easy Tips To Help It Bloom

Duncan Corals are gorgeous additions to your tank. Their swaying tentacles and sprouting heads make a wonderful display in your tank. So naturally, it’s worrying if your coral remains shut.

Is there a solution to Duncan coral not opening?

Yes, there is! Your Duncan coral isn’t opening due to sprouting new heads, environmental changes, or feeding issues.

These can simply be helped by routine checks, adjusting the water, the position of the coral, and spot-feeding the coral.   

Now, if you have the time, we have a complete guide. All the details about your Duncan coral have been fleshed out for ease. 

How Long To Wait Before Helping Duncan Coral Open?

Exactly how many days do you have to wait before it gets worrisome? It’s completely normal for your Duncan Coral to take time to acclimatize.

This is especially true if it’s new to the tank. Give it a day or two, and it should open up just right. 

Duncan Corals can be a little moody. So even when everything’s alright in the tank, your Duncan may remain closed.

But, it should open up within 2 to 3 days, which is normal.

It’s too long if it doesn’t open up for 2 to 3 weeks. This could be a sign of trouble and needs investigation.  

But exactly what is it that you’re looking for? We’ve listed out all the things below.

Why Is My Duncan Coral Not Opening?

There are a few possible reasons why your Coral isn’t opening. Most of these are easy to identify and take care of.

Sprouting A New Head

This is the most common reason. When your Duncan Coral wants to sprout a new head, it’ll close up. This way it can carry out all the physical processes and conserve energy.

If it’s sprouting, the process will take a week. After that, the Coral should open up. 

Constant Checks

If the Duncan coral is sprouting a new head, you must be patient. Carry out daily routine checks and see if there’s any change.

By day 5, you should see some activity, and by day 6 or 7, the coral should open. 

If your coral doesn’t open, then opt for a check. Use a reliable nitrate test to check for nitrates and carry out a phosphate check.

Lack Of Nitrates

Water chemistry is one of the most crucial factors for any coral. Duncan corals are the same. A lack of nitrates in the water can cause them to close up.

This can be a distress signal as Duncan Corals like nutrients in the water. This helps them thrive in their natural habitat. 

Let The Tank Brew 

After carrying out a nitrate test, if you see that it’s undetectable, leave the tank. It can be for a day or two. This will help elevate the nitrate levels naturally.

Once this happens, your coral should detect the change and open up.

This is because many of these corals prefer slightly elevated levels, between 0.3 and 0.5. These nitrate levels represent their natural habitat.

The Water Flow Conundrum

Duncan corals prefer low to moderate flow. Replicating this in a tank can be difficult. Your corals may close if it feels stressed out under the flow it is in. 

This can be tricky to detect because other corals in your tank may be fine. But only your Duncan coral is the one not responding.

Change The Position Of The Coral

If there’s confusion with water flow, try moving the coral. Over the week, relocate your Duncan coral in the tank.

Opt for lower places that have subdued lighting. These are natural conditions for Duncan Corals, so they should open after a day.  

High Temperature

While you may have the best heater for your tank, it might not always be a good thing. Duncan corals like cooler waters. This helps their polyps and tentacles expand better. 

If the temperature is too high, there is a chance of bleaching. Thus to protect the polyps, the coral may remain closed.

Let It Cool!

If the water temperature is too high, above 80 degrees Fahrenheit, it’s better to cool it. Do this cautiously because you don’t want anybody in the tank to stress out.  

Do this slowly for a week. Slowly reduce the temperature and leave the tank for a day to see how the coral responds.

Once your Duncan coral opens, you have the right temperature. Normally this temperature will hover between 76 to 78 degrees Fahrenheit.

Troubling Mates And Feeding Issues

Overfeeding is always troublesome. Even more so with Duncan corals because they tend to be aggressive.

Their polyps and tentacles can grab food meant for others, and overeating can cause them to close.

Additionally, food can accumulate on the coral. This can attract mates in the tank who’ll pick on the food.

If it’s done by aggressive fish in your tank, it can stress and close the coral.

Solution 1: Reintroduce The Mates And Change The Feed

If your mates are aggressive, try reintroducing them into the tank. You can schedule this with a water change so that there isn’t any additional hassle. 

Meanwhile, clean your Duncan coral. Once the mates are reintroduced, see if it opens up. If it does, you’re all good to go.

However, if the coral still doesn’t open, you may have to change the feed in your tank. If the regular algae feed isn’t working, you can always opt for foolproof algae wafers.

This should keep your mates busy and away from the Duncan coral. 

Solution 2: Spot-Feeding

If there are too many algae in the tank, it’s best if you clean it up. A simple water change should do the trick.

Additionally, you could try spot feeding. This way, you can control how much food your coral is getting.

If you’re spot-feeding, do so three times a week. The rest of the week, should be fine.

If you’re wondering what to spot-feed your Duncan coral, it’s simple. Opt for foods like nori, salmon, prawn, and blended flakes.

Make sure the pieces are small enough for your coral to grasp.

Suppose you’ve made it this far; great! We’re almost at the very end.


Question: How long does Duncan Coral take to open?

Answer: Depending on the tank parameters, your Duncan coral should open within one to three days. To fully acclimatize, you should look for a week.

Question: Why did my Duncan coral die?

Answer: If your Duncan coral has died, it could be an infection or algae. Algae can grow on polyps. If that happens, the polyps won’t be able to photosynthesize, and they’ll die.

Question: Are Duncan corals hard to keep?

Answer: While Duncan corals can get aggressive, they are easy to take care of. You need to make sure that they are kept within moderate flow and lighting. 


We hope you know all you need about the Duncan coral not opening. Let us know if these tips helped your coral open up.