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Why Your Zoanthids Are Not Opening!

With the popularity of zoa only tanks drastically increasing over the last year due to their unique look going viral on social media, the popularity of keeping zoanthids in various types of aquarium has also seen a large spike too.

Thankfully, zoanthids are usually one of the easier corals to keep as they are very beginner friendly but we have seen a number of people having problems with their zoanthids not opening up correctly so we wanted to go over some common problems to try and help our readers.

The most common reasons that zoanthids will not open in an aquarium are due to problems with water parameters and harassment from their tank mates nipping and eating them.

Less common problems that can stop your zoanthids from opening up also include problems with salinity, water flow, nutrition, lighting, and the placement of your zoanthids with all problems generally being easy to fix.

Due to the spike in the popularity of zoanthids growing exponentially recently, there are a number of people selling weaker zoanthid coral frags that are more susceptible to various problems.

Always try to make sure that you go with a healthy zoanthid frag if possible as they tend to be far more robust and hardy increasing the chances of the zoas opening up even in conditions that are not optimal.

How Do You Know if Your Zoanthids Are Dying?

It is usually pretty obvious to see if your zoanthid corals are dying as their normally bright colors tend to rapidly fade, they take on the melting appearance rather than their normal free flowing appearance and they can eventually look more like slime algae than coral.

If your zoanthids have not opened then this is not always a sign of the zoanthid dying and it could just be a sign of temporary problems with most zoas being able to make a full recovery.

If your zoanthid coral is not opening but you also see some of the other signs that indicate there is a potential problem in your aquarium then you really do need to investigate as soon as possible.

We have dedicated articles on how to stop your zoanthid melting and what to do about zoanthid pox outbreaks in your tank that should be able to help you if you do see signs of this.

A closed zoanthid is usually just an early warning sign of a potential problem in your aquarium though and provided you catch the early warning signs quickly, you should be able to correct the problem and help your zoanthid open up and live a healthy life moving forward.

If you can see signs of damage, usually due to fish, shrimp or crabs eating your zoanthid then something as simple as removing the offending tank mate or putting the zoa coral into a different tank can be enough to correct the problem.

How Long Does It Take for Zoanthids to Open Up?

There is no set timeframe for a zoanthid coral to open up as the water parameters, lighting intensity water flow, and nutrition levels in your tank all come into play.

Some zoanthids can open in as little as a couple of hours where as some can take days and in rare cases over a week but anything longer than ten days is usually a sign that there is a problem in the aquarium.

You can usually confirm that there is a potential problem as your zoanthid growth rate will be considerably slower than usual too.

You also have to keep in mind that zoanthids in the same aquarium placed very close to each other can have totally different opening timeframes too as they can get very different levels of water flow and light intensity so always try plan this prior to placing your zoanthids.

Thankfully though, zoanthids do tend to be fine with you reseating them in a new area in your aquarium when compared to some other more sensitive corals.

This means that if you do realize that you have made a mistake with your initial zoanthid placement and it is getting too much light and water flow then you should be able to move it at least once without issue to reduce the exposure to the potential problems.

Why Are My Zoanthids Closed?

You will usually find that your zoanthids are closed due to having problems with the water parameters, tank mates eating them, having high water flow, and light intensity problems.

In some situations, salinity levels and nutrition levels in the tank as well as the placement location of your zoanthid in your aquarium can all come into play with some tanks having problems with multiple things at the same time.

This is why it is so important to check for all possible problems that could potentially cause your zoanthid to not open.

We have seen a number of people report that they found problems with their water parameters as its the main thing most people check for and presumed that was the issue, fixed the problem, and their zoanthid failed to open due to there being secondary problems in the tank too.

Another thing that we commonly see people make mistakes with when it comes to their zoanthid water parameters is that they use a generic water test kit that doesn’t test all water parameters and is commonly inaccurate in the things that it does test for.

This can make you think your water parameters are optimal for your zoanthid to open when in fact, they are far from it so always use a decent reef tank test kit to make sure you are getting accurate readings and testing for everything that can potentially cause problems with your zoanthid.

How Can I Get My Zoanthids to Open Up?

You can usually get your zoanthid to open up by making sure the water parameters are in line with what a zoanthid requires, check that you have medium water flow, and that your light intensity is at a medium setting, especially your white light with blue light often being fine at a higher setting for zoanthids.

If you don’t know that your tank has the correct nutrition in it to correctly feed a zoanthid then provide additional nutrients as required too.

There are a number of different coral food options on the market these days but one of the better ones is reef roids that is excellent at helping a new zoanthid in a tank get plenty of nutrients.

Some people also supplement a zoanthid that is not opening with a Vitamin C supplement too and although there is correlating evidence to suggest that this can help a zoanthid to open up, it does not seem to be a reliable fix.

Some tank mates, even ones thought to be reef safe can eat chunks of your zoanthids due to them being a softer coral.

You should look for signs of something eating your zoanthid and remove the coral or the offending tank mate if possible as nips and bites will keep your zoanthid closed.

You can usually get an idea if the offending tank mate is a fish or shrimp/crab by the damage to the zoa as fish tend to have a feathery break where they bite as the coral fibers are left there but shrimp and crabs usually have a clean break.

What Should I Do If My Zoanthids Are Not Opening And Shrinking?

If your zoanthid is not opening and starting to shrink then this is a reliable indicator that your zoanthid is dying so you really have to investigate possible problems that could be causing the issue.

This is generally a later stage warning sign of a problem and if you have accidentally left it to this stage before trying to find the problem then it may, unfortunately, be too late to recover your zoanthid.

A zoanthid not opening and shrinking can also be due to inconsistent water parameters in the tank too.

This can be a common problem for beginners and will usually involve you fixing the problem and your zoanthid opening up only to close again a week or two later with the cycle just repeating over and over.

If you do have this repeating cycle with your zoanthid then you can try to increase the frequency of your tank maintenance schedule, especially if you are not currently cleaning your tank at least once per week.

There is a decent chance that the problem is due to a spike in at least one water parameter, often nitrates due to a lack of cleaning that then causes your zoanthid to close.


That brings our article going over why your zoanthid is not opening to an end. We hope that we have been able to help you better understand the potential reasons that your zoanthid is not opening and that you are able to get your coral to open up. You will usually find that your zoanthid will open up within around a week of fixing whatever problem was keeping it closed so you can usually get some quick indications of if you have fixed the correct issue in your tank.