Why Do My Zoanthids Keep Melting?

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If you bought a nice frag of zoanthids, and they settled nicely in your reef tank at first, but then they suddenly started shrinking and melting, you are not alone.

Zoanthids are easy corals to keep but sometimes, out of nowhere, they start melting and disappear entirely. It’s very frustrating when that happens, especially if you bought an expensive coral.

I keep zoanthids in my reef tank, and I didn’t have any problems so far. However, I was aware that it might happen eventually, so I acted proactively.

I researched, gathered other hobbyists’ experiences, and learned why zoanthids shrink and what you need to do to prevent zoas from melting.


Why do my zoas keep melting?

There are a lot of reasons why zoanthids melt away. Here are some of the most common ones, but keep in mind that zoas may melt away for other unknown reasons.

Water Parameters

When you notice your zoas start shrinking and melting away, the first thing you should check is your water parameters. 

The key to a healthy reef ecosystem is stability. Don’t chase numbers, and make sure that there aren’t big swings in your parameters. Large alkalinity swings may cause your zoanthids to start melting.

Test your water regularly and keep a reef log of all your measurements. It’s the best way to prevent problems before they even happen.

Low Nutrient Systems

It seems that zoanthids won’t thrive in ultra-low nutrient systems. It is no surprise because they are usually found in dirtier waters. 

Make sure that your reef tank has detectable levels of nitrates; otherwise, you might see yourself in trouble keeping zoas alive.


Zoanthids are adaptable to a wide range of lighting. You can keep them in low light, but in my experience, they do better under high light. 

When you purchase a frag of zoanthids, make sure to match the light intensity from the place you bought them, then slowly acclimate them to your desired location.

Zoa Eating Nudibranch

The zoa eating nudibranch is a pest that feeds on zoanthids. We will not talk about the zoa eating nudibranch in this article because we have a dedicated article on this subject. 

Feel free to check it out: How to get rid of the zoa eating nudibranch?

In essence, it is not something you want in your reef tank.

How to save melting zoas?

It’s challenging to save zoas that have already started to melt away. It’s usually a point from which there is no coming back. 

However, there’s something you can do to prevent some common zoa problems that may harm them in the long run.

Remove algae from the frag

Sometimes frags come with a little bit of algae. Gently brush your frag with a soft toothbrush and try to remove as many algae as possible. Your zoas will have a better chance to survive and spread in your reef tank.

Dip the zoanthids

Always dip your zoas before introducing them to the main display tank. With coral dipping, you remove most of the unwanted pests that may cause you many headaches in the future.

Quarantine your zoas

The best way to prevent a major disaster is to quarantine your corals before introducing them to your display tank. 

Keep in mind that some issues might not present themselves right away, so monitoring your corals in quarantine for a couple of weeks is always a good idea.

Related: Zoanthids Growth Rate| How to Make a Zoa Garden| Zoanthid Coral Care

Final Thoughts

It’s very frustrating when your favorite zoanthids start melting away. And for some reason, they always seem to be the most expensive ones. Don’t despair. Sometimes whatever we do, we cant save them.

Make that your water parameters are on point, quarantine and dip every coral you buy. That’s everything you should do from your end.

And if nothing works and every zoa you buy always melts in your tank, then don’t buy zoanthids. Easier said than done.

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