Why Are My Zoanthids Not Opening? Possible Reasons & Solutions

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You bought a frag of zoanthids, and they are not opening? You don’t need to worry because, in this article, I will cover all the reasons causing zoas to close. In addition, I will provide several solutions that might help you with these problems.

Zoanthids are one of my favorite corals because they are easy to keep, come in different varieties and shapes, and are colorful.

When I first got into the saltwater aquarium hobby, I was hesitant to buy zoanthids. All the stories I’ve heard about these corals and the danger of keeping them have pushed me away for a long time.

However, I learned that zoanthids don’t possess a threat as long as I handle them carefully.

I bought a small frag of radioactive dragon eye zoanthids to see whether my tank is ready. The following month, I’ve bought other zoa frags, and I intend to buy more. I want to create a beautiful zoa garden.

During the months that I’ve kept zoanthids, I’ve encountered some problems, mainly with zoas not opening. I overcame all those problems, and, in this article, I will explain how.

Let’s get started!


Why are my zoanthids not opening?

Zoanthids may take several days to a week to fully open in a new environment. Other reasons may cause zoas to close, such as poor water quality, pests, and sudden parameters swings.

Adjusting to new conditions

The first zoa frag I bought opened imminently. The second frag took two weeks to fully open, and the third one a week. 

As you can see, there aren’t any rules on how long it needs for zoas to open in a new tank. 

As long as your water parameters are adequate and there isn’t a pest bothering them, your zoas will open. It might take a day, a week, or two, but they will open.

Poor water quality

If your water parameters are not on point, I am afraid your zoas might struggle to open. Zoanthids need stability just like any other coral.

Test your water parameters regularly. I can’t stress this enough. Do weekly water changes to replace the trace elements.

Make sure that you have detectable nitrates in your reef tank. Zoas thrive in nutrient-rich environments. They collect zoanthids from one of the dirtiest waters in the reef and might struggle in sterile environments.

Placement & Water flow

In my experience, zoanthids can adjust to any place in your reef tank. 

However, be careful with new additions. Place them on the sandbed and slowly adjust them to a higher position.

Sometimes zoanthids might close if they are in a high flow area. Consider moving them to a low flow area and see whether they start opening.

Whenever you move your zoas, wait a while to see if there is any change. 

Constant moving can also irritate zoanthids.


Everybody wants an algae-free reef tank, but the reality is we all had a problem with algae outbreaks at some point in our reefing journeys.

It’s the worst when algae are covering one of our precious corals. Zoanthids covered in algae won’t open.

There are several solutions to this problem. Take out the frag from your reef tank and remove the algae manually. 

Be careful zoanthids contain palytoxin. Always wear gloves and eyewear, and don’t do this if you are a beginner.

In addition, you may use a hydrogen peroxide dip to remove the algae from the frag.

All these solutions won’t be enough if you won’t solve the nutrient issue in your tank, the reason to have algae in the first place.


Of all the corals in the saltwater aquarium hobby, zoanthids have the most types of pests.

That’s why it’s essential to dip your zoas before you put them in your main display.

The most common zoanthid pests are the zoa eating nudibranch and the zoa eating spider.

Additionally, you should avoid getting fish such as angelfish, butterflyfish, or rabbitfish because they might eat your zoas.

How long does it take zoanthids to open?

It can take a couple of hours to a week for zoas to open in a new tank. It depends on many factors.

As I’ve mentioned earlier in this article, I’ve had zoas that had opened right away and zoas that took two weeks to open. Different types of zoas will open at different times.

If your water parameters are on point, your zoanthids will open.

Are my zoanthids dying?

Zoanthids can stay close for weeks and then open and spread like crazy.

However, if they start shrinking and melting, they will probably die. There are a lot of reasons why zoanthids start dying. Sometimes even, there is no reason at all.

It’s challenging to save zoas when they start to melt away. The best way to preserve your zoas is to find the underlying issue causing the melting.

Final Thoughts

Whatever I do, there always will be some zoas in my tank that are unhappy. Even polyps from the same colony may act differently.

However, when I see that most of my zoas are closed, I act immediately. 

I test the water parameters, make small water change, and carefully observe the tank. It’s what you should do, too.

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