Why is My Green Star Polyps Closed & Not Opening?

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Green star polyps closed and not opening? Learn the main reasons and what you can do to get your GSP coral open.

Last year I got into the saltwater aquarium hobby. I hesitated for years, but in retrospect, it was one of the best decisions I have ever made. I might say that I enjoy this hobby and learn new things every day.

The main goal with this hobby was and is to keep corals. Even though I had previous experience keeping freshwater tanks for almost 20 years, corals were unknown territory.

I decided to start lightly and buy hardy and easy-to-keep coral. I purchased a green star polyp, the most recommended coral for beginners.

My local fish store has an excellent collection of corals, and it’s only ten minutes away from my home. It was a no-brainer to go and get my coral in person. I chose a healthy-looking specimen of green star polyps and was home in no time.

As the fish store owner told me, I acclimated my coral and started observing it, hoping it would open soon. The owner said that it could take a couple of days for the GSP to open fully.

However, my green star polyp stayed closed for almost a week.

As you can see, the above picture is of my fully closed green star polyps. It’s not even closely represent the beauty of a fully extended green star polyp. It’s just a bland purple mat.

And here’s a picture of an open GSP. It’s the same coral, only one week later. As you can see, there’s nothing to worry about, and your GSP coral will open eventually.

However, keep in mind that certain things may irritate your coral and cause it to never fully open. Keep reading to find out the most common reasons GSP coral is not opening.


Reasons why GSP coral is not opening

Why is your green star polyp closed and not opening? Here are the most common reasons.


It is common for corals to stay closed for a prolonged period when they change the environment. The green star polyps are no exception. They are hardy coral, but in my experience, they have a temper.

When I got my green star polyps, it stayed closed for almost a week. I acclimated adequately, placed it on a good spot, and still waited for a week to open. Even today, my GSP sometimes randomly closes and stays that way for a couple of days. 


In my experience, green star polyps will grow anywhere you place them. In fact, you need to think twice before you add green star polyps to your tank. 

If you are not careful, it will populate your whole tank in no time. These corals spread very fast. Make sure that it is placed on an isolated rock, so it can’t spread all across the tank. 

Also, find one position and try not to move it all the time. If you constantly move your GSP, it will stay closed for a long time.

Flow & Lighting

Green star polyps are hardy coral and can thrive in various conditions, but it doesn’t mean you can throw them in a tank without proper light and flow.  

Improper lighting and not enough flow can also be one of the reasons why your GSP is not opening. 

Luckily, there are very cheap and affordable lights and wavemakers on today’s market, with which you can keep green star polyps or any other soft corals in your tank.

GSP prefers moderate flow and lighting, so make sure that those factors are not the reasons for your coral to stay closed.


When I bought my first coral, I made the beginner mistake of not dipping corals. To my surprise, after a day, many new organisms start to pop up in my tank. 

I bought a green star polyp, but I got a bristle star, bristle worms, and a lot of different miniature organisms. Many of these organisms may crawl on your coral and irritate it, causing it to stay closed.

Water Parameters

All the reasons mentioned above don’t matter if your water parameters are not on point. 

Before looking for other reasons, make sure that your parameters are ok. Don’t chase numbers, just make sure that your system is stable and your GSP will open as soon as possible.


Sometimes algae could irritate your coral and cause it to close. In that case, take a soft toothbrush and slowly clean the purple mat. 

Don’t worry the purple mat is hardy, but make sure that you are not applying too much pressure. 

Related: Green Star Polyps Care Guide

How to get green star polyps to open?

Green star polyps is a very hardy coral almost impossible to destroy. It grows very fast, and if you are not careful, it will populate your whole tank in no time.

Some people love GSP; others consider them pests. If you have trouble keeping a GSP alive, you are doing something wrong.

For starters, make sure that your water parameters are always on point and don’t fluctuate a lot. Like any other coral, GSP loves more stability than chasing numbers.

When I stopped messing around and moving my GSP all across the tank, my GSP opened. After one week, the green star polyps in my tank were fully open and acclimated to the new environment.

Have patience, and if all the other parameters are on point, your green star polyps will open in no time and start spreading fast.

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