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Why Are My Zoas Closed And Not Opening Up

By April 4, 2020No Comments
why are my zoas closed

Why Are My Zoas Closed

Zoas are one of the most popular corals for reef tanks. But sometimes they do not act right, and you just want to figure out why are my zoas closed up. This may not be an easy solution, as there can be so many different factors causing them to not open up.

We will cover multiple reasons so hopefully your zoanthids will spring back to life again.

Zoas are often listed as a beginner coral, so many new hobbyist start out with them. For some, they are easy going with no issues, for others, they can be finicky. Lets take a look at some things that we can do to help them open back up again. What we are looking at is being closed for an extended period of time, not because a crab or something else disturbs them.

Here are some of the reasons that your zoas may be closed up:

  • Pests
  • Nutrients
  • Incorrect lighting
  • New To Your Tank
  • Incorrect Flow
  • Bad water paramaters
  • Stray Electrical charge
  • Allelopathy
  • Location

Pests Can Keep Zoanthids Closed

One of the first things to check for on your zoas are pests. Hopefully, any new coral that you have acquired has been treated with a dip and been quarantined.

Here is a list of the common pests that are found on zoa colonies:

Sun Dial Snails can be a terror to zoa colonies. If you notice that one by one your zoas are going down, this is a good sign. These like to stay hidden in the polyp and come out at night.

Asterina Starfish should be easy to spot and they need to be removed.

Zoanthid Eating Nudibranchs are tiny little pests that will sometime take on the color of your coral which makes it harder to see them. If you find them, it is also likely that you have eggs as well.

Zoa Spiders are eight legged creatures that look like a tradition spider. They are about 5mm in size. A lot of coral dips do not kill them, so the best method is quarantine and removal with tweezers.

Bad Water Parameters

This should be easy to figure out, as most things can be tested. Some standard parameters for Zoas are:

72-78° F, dKH 8-12, sg 1.023-1.025, pH 8.0-8.4

Incorrect Nutrients and Zoas

Two of the most measured and observed values in reef tanks are Nitrates and Phosphates. While some may believe that zero is the goal to shoot for, low nutrients can cause you zoas to close up. Many reefers note on forums and social media that their zoas like the water a little “dirty.” While we know that high nitrates and phosphates are not a good thing, neither is absolute zero on both of those.


Wait, what? Basically, chemical warfare. It is always a good idea to understand all your corals and placements for each. Sometimes a zoa might be too close to a neighboring coral that is emitting toxins and being territorial. Take a look at your colony or frag and see what is near it and research to find out the compatability.

New Environment

Are your zoas new to your tank? If so, they may need to adjust to their new environment. I have seen some open within a few hours, some open back up after a few days, some open at first and then stay closed for awhile. Either way, give them a couple of weeks to get used to the new surroundings. Moving them around every couple of days because they won’t open up is usually not the best way to approach this situation.

Incorrect Flow

Zoas can adjust over time to lighting and flow in your tank, but more often than not, I have found that a higher flow will help zoas open back up. A low flow over your zoanthids can increase the chance of them become “unhappy” which makes them more prone to disease and algae, etc. Try placing your frag in a place with a little more flow.

Incorrect Lighting

If your new colony remains closed, and they came from a lower light environment, they may be stressed due to higher light at the placement in your tank. Try moving them to a more shaded area for a few weeks to get them acclimated to the higher lighting in your tank. I have seen a case where a frag was exposed to high white light for a day. The colony closed up for several months, then new polyps came out and eventually the older polyps came back. If you accidentally blasted them with very high light, give them a lot of time to come back.


Sometimes, you may just have a frag or colony that does not like it where they are placed. If you can rule out other issues, this may be a simply case of “please move me somewhere else, I don’t like it right here.”

Stray Electrical Charge

This is probably a rare occurrence, but several reefers have mentioned this as a cause for closed zoa colonies.


Zoanthids are one of the most mentioned beginner corals, so they are very popular, and this means they are especially popular with new reef tank owners. One of my first purchases was a zoa frag and it gave me lots of problems for about 5 months. I spent tons of money and hours of research trying to figure out why they would not open.

It all came down to the fact that I didn’t know what I was doing with my new tank, so there were several reason why they stayed closed for so long. The problems were multiple. Incorrect lighting, incorrect flow, and bad water parameters caused the issue.

I did not understand the role of phospates in my aquarium, the importance of RODI water, and I did not understand lighting parameters. I constantly moved my frag around stressing it more. My new frag was placed in a low flow area, my phosphates were high which caused algae issues, and even caused algae to grow on my plug and the closed polyps.

I moved it to a new location with higher flow, researched lighting and adjusted, and added GFO to reduce phosphates. Algae went away, scum left my polyps and they all eventually opened back up. The issues came down to bad water parameters, bad flow location, and improper lighting.


My name is James, and I am the founder of Saltwatercoraltank. I love everything about the ocean, and my main hobby is saltwater aquariums. Currently, I have 3 tanks that I maintain. I have a 130 gallon mixed as my main, and I prefer softies.

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