Zoanthids Not Opening? – Find Out Exactly Why

If you are new to keeping Zoanthid corals, a common concern is they tend not to open from time to time.

But don’t worry, zoanthids are a hardy coral and they are great for beginners. Caring for Zoas is generally easy providing you give them what they need to stay healthy.

zoanthids not opening

If your Zoas are not opening, there are a few reasons why this might be happening.

In this article, I will show you how to help your Zoas to open back up and prevent it from happening in the first place.

Why are my Zoanthids not opening?

There are a few reasons why your Zoanthids are not opening. For me, the biggest reason I see this happening is due to an invertebrate like a hermit crab or cleaner shrimp crawling on them. Zoas are not a fan of that.

It’s very common to see certain inverts walking or running across a colony of Zoas. This will cause the coral to close up and it might take some time for them to open again. But normally it doesn’t take long.

Also, it’s possible that a fish could be picking at the Zoa making it unhappy and not opening up. I had a Yellow Tang once that was bothering my Zoa colony so much I had to move it into another tank. This is not overly common but it does happen from time to time.

Another reason your Zoas are not opening could be your water parameters. If your salinity is fluctuating or any other level such as PH is off, this will cause them to stay closed up. Once you test your water parameters and adjust anything that is not within limits, the Zoas should open again nicely.

If your Zoanthids are new to your tank, it might just take some time for them to get acclimated and comfortable to the new environment.

How long for new Zoanthids to open?

If you introduce new Zoanthids to your reef tank, it will take some time for them to open up. Sometimes this happens quick but other times it can take a few days to possibly a couple of weeks. You should always acclimate your new corals to the tank to help them get used to their new environment and conditions.

Zoanthids water parameters

Zoanthids are generally a tough coral and can survive in less than pristine environments. But you always should make sure that your water parameters are within the proper range to ensure the coral stays healthy and grows properly.

It’s important to maintain constant water temperature for Zoas. They don’t like fluctuations. Aim to maintain a 78F temperature. PH should be 8.0-8.4 and salinity of 1.025.

Other water parameters to check are magnesium, calcium, alkalinity.

Here is a chart to reference.

How to know if Zoanthids are dying

If your Zoanthids are no longer opening up for a long period of time, losing color, and look like they are melting away, it could be a sign of them dying. Zoas are pretty tough though so don’t give up on them. I have seen some pretty bad looking Zoas that I thought for sure were not going to make it that ended up being fine over time.

Here are a few things to look for:

  • The Zoa Polyp will appear to be collapsed and wilting over.
  • Disintegrating polyp that could shred apart.
  • Not full-bodied with a foul odor.
  • Dark pigment and coloration. 

Zoanthids health tips – feeding, light, water flow

Zoanthids dying

To prevent your Zoanthids from not opening properly, it’s important to follow some general health tips. 

Feeding – Your Zoas will benefit from periodic feedings. Target feeding is a great idea and can be done a few times per week. They will appreciate certain foods like brine shrimp, plankton, krill, and copepods

You can use a target feeder like this one on Amazon.  

Zoanthids are also able to grab food from the water column so if you decide to not target feed, go with a coral food such as reef roids where you can mix with water and pour into a high flow area of the tank. 

Because Zoanthids have a photosynthetic partnership with Zooxanthellae, it is not necessary to feed them but it will help them grow, maintain colors, and stay healthy.

Lighting – Zoanthids can survive in a variety of lighting conditions. They do prefer a medium to high lighting which will allow for their polyps to grow and show more colors. But be careful that the light is not too intense as this can cause them to lose color fast.

Use a quality reef LED light, T5, or metal halides for your Zoas. Some of the best colorations from Zoas are seen using blue actinic LEDs or bulbs. It really makes the colors pop in your tank.

Water movement – Zoanthids prefer a low to medium water flow that has a varied pattern. If the water flow is too high, they will have a difficult time opening their polyps which will have serious health effects on the coral. It’s better to have a lower flow than high flow for Zoanthids. Once you notice the coral polyps opening and their colors really showing, then you know it’s the right flow for them. They will let you know if the flow is not acceptable for them. 


So if your Zoanthids are not opening, check to make sure it is not being bothered by other tankmates. Fish and invertebrates can annoy them at times. Also, confirm that your water parameters are within the proper range, and ensure you are providing adequate lighting and water movement.

If your Zoanthids are new to the tank, just give them some time to get used to the environment. Sometimes this can take a couple of weeks or perhaps just a few days.

With proper care, you won’t have a problem with Zoanthids not opening properly. They are an amazing coral that are very popular among saltwater hobbyists. With over 100 different types available, it is not difficult to find ones that suit your tank perfectly!