Duncan Coral Not Opening? Possible Problems & Solutions

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Your Duncan coral is not opening, and it’s all closed up? You don’t need to worry because this article will help you solve your problem. It’s from personal experience.

duncan coral not opening

The Duncan coral is my favorite coral in my reef tank, even though I say that for most of my corals.

Kidding aside, the Duncan coral really has a special space in my heart. It was one of the first LPS corals in my reef tank and one of the corals that got me into this hobby.

During this period, I had been with the Duncan coral; I have seen it closed up several times (not counting the nights) without reason.

At first, I was afraid whenever I saw the Duncan closed up. I often thought to myself: that is, this coral is gone. But I’ve done the research and learned about the reasons that cause Duncan corals to close.

If you want to learn too, keep reading. In this article, I will explain all the possible reasons why your Duncan coral is not opening and give you several solutions.

Sounds good enough? Let’s get started!


Why is my Duncan coral not opening?

Duncan corals may close up from time to time, and that’s perfectly normal. However, the Duncan coral is the first indicator that something is wrong with your water parameters. You better check it out.

Duncans are very hardy corals. They won’t die overnight unless you have a major tank crash. However, they can be moody. Duncan corals can go through phases of fully open to close throughout the day.

How long does Duncan coral take to open?

After you’ve introduced the Duncan to your reef tank, it might take a couple of hours to a couple of days to fully open.

When I put a Duncan in my tank, it took a whole day to open. It didn’t fully extend until I found its perfect position. You should not worry if it takes a couple of days, assuming all your water parameters are on point.

Remember, the Duncan probably lived under different lights, flow, and water parameters in its other home. It might take a while to get accustomed to your tank conditions. 

Duncans are hardy corals and will get accustomed to most tanks.

duncan coral

What causes Duncan coral to close up?

There are many reasons why Duncan corals close for a prolonged period. 

Most of the time is nothing serious, but Duncans are excellent indicators of what is wrong with your water chemistry, so you better keep an eye on it.

Here are the most common reasons:


These corals prefer moderate flow and lighting, but that’s too vague. 

What is moderate?

My Duncan came from a tank with a high flow. It looked good, but it wasn’t fully open. When I put it in my tank, I tried to replicate the same conditions and place it in a higher flow area. 

But it still wasn’t fully open, so I decided to move to a low flow area. The next day the Duncan coral looked incredible. What is my point with this story, you might ask?

Try to move your Duncan to a lower flow area and observe. High flow might be the reason why your coral is not opening.

Water Chemistry

They say that Duncans are great indicators of your water chemistry, and when something is a little off, they close up. It’s true.

Duncan corals often close when there are alkalinity swings. When your Duncan suddenly closes up, do yourself a favor and run some tests. It’s the only way to know whether your parameters are on point.

Sprouting New Heads

Sometimes these corals close up when they are sprouting new heads. If this is the case, you should not worry at all. Your Duncan will soon open and grow bigger than it was.


Duncans can stay closed for a prolonged period when there aren’t enough nutrients in the water. Always keep your nitrates above 0ppm. 

In my experience, Duncan thrives in a nutrient-rich environment. 

However, don’t go overboard because high nutrients may cause other problems in your tank.

Someone Bothering It

Clownfish loves to host Duncan corals so much that they might bother them enough to cause them to close.

You can’t do anything about this except move the clownfish or the Duncan to another tank.

Keep a close eye on your other tank inhabitants to see if anything else bothers your coral.

Final Thoughts

My Duncan coral is moody and sometimes closes up without any reason. 

Based on other people’s opinions, it’s probably a universal thing.

You should not worry if it occasionally closes, but you should test your parameters every time it does it. 

Duncans are hardy corals, and whatever the reason is for the closing can be solved.

1 thought on “Duncan Coral Not Opening? Possible Problems & Solutions”

  1. Hello, My plumpy Duncan’s have been closed for a couple of days. I did a water change and tested as well. Parameters are spot on. A ricordia and a rock flower nem are also semi-closed. The snails in the tank have also died off. The hundreds of pods living in the rock work and sand are fine. Emerald crabs are fine . It’s a mystery


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