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Green Star Polyps Closed And Not Opening

By January 16, 2021No Comments
green star polyp coral

Green Star Polyps (Pachyclavularia violacea) are beginner soft coral that look amazing in reef tanks. These corals are easy to care for, and they are perfect for inexperienced reefers, but as with any coral, there can be times when they stay closed.

GSP are a love/hate coral for a lot of reefers due to their fast growth rate. They are an encrusting species, so they will completely cover about anything you put them on. They can be used as a living mat for a back wall, an overflow, tubes, pipes, rocks, etc. While this may be desired for some saltwater aquariums, it can also be considered invasive to others.

There can be a variety of reasons why GSP’s will not open, but once you go through the common issues, your corals should be looking great again.

Green Star Polyps will stay closed and not open up due to a variety of reasons including placement, flow, lighting, algae, and bad water parameters. The most common reasons that they will not open are salinity, flow, and incorrect placement. Bad placement by itself can cause multiple issues with green star polyps being retracted.

Here is a list of the main reasons that green star polyps will not open up, and we will review how to troubleshoot and correct this problem.

  • Placement
  • Incorrect Tank Setup
  • Flow
  • Algae
  • Disturbed By Fish And Critters
  • Salinity Is Off
  • Acclimating
  • Pests


One of the most common problem with any coral frag including green star polyps is where they are placed in your tank. Placement choice can cause a lot of different issues which we will also review in this article. The great news is that these soft corals are hardy, and if you are not seeing them open up, you can just move them. We have seen corals like zoanthids that were placed too high in an aquarium and got too much light which damaged them. It took several months for them to open back up.

So many other variables like lighting and flow are affected by where you put your frags, which is why it is imperative that you find the best spot for your GSP’s.

Green Star Polyps like some flow and moderate lighting. You should have enough current around them so that you can see them moving in the water.

These corals are placed in a lot of beginner saltwater aquariums because they are inexpensive, and they grow really fast. People like to have their reef tanks look proper, and a lot of corals take so long to grow out and cover live rocks. Because they are so common with beginners, there are a lot of placement issues that come up.

Incorrect Tank Setup

As we discussed, these corals are purchased a lot for beginners which means newer tanks. Having a saltwater tank can get expensive especially with equipment, and sometimes people can take shortcuts with lights and powerheads. This is certainly understandable, because the cost can get out of hand when you are building your first tank.

While, you don’t need the most expensive lights for green star polyps, you still need something better than a $30 strip light that works on a freshwater tank. If you feel that you may have inadequate lighting, then reach out to your local fish store or an online vendor to find out what the best low cost option would be for you.

The same goes for power heads and circulation. You need to have good flow in your aquarium. Stagnant spots in your tank are not good for many different reasons. These corals need enough flow around them to have some movement. You don’t need the best powerheads, but these corals do much better with movement, and you need to have the equipment set up in your tank.


These soft corals like flow, and if they are not getting it, they may close up. Have you made a recent change to anything in your tank to affect the flow? If you have recently moved your powerhead, this would probably explain your issue.

Also, if you powerhead is pointed right at your colony, it may be receiving too much direct flow. You will need to move your coral or adjust the angle of your powerhead.

A lack of flow can cause sand and detritus to settle on the gsp mat. The dirt and poop on the mat can irritate the polyps which can keep them closed. To clean it off, just blow it off with a turkey baster.

If your coral is not receiving enough flow, it can run a risk of getting brown algae on it. Algae can cause problems for any coral.


Often, when algae gets on a colony, it will stay closed and not open up.

To clean algae off of green star polyps, you can use a turkey baster on them to make sure they are all fully closed, and then you can lightly clean it with a soft bristle tooth brush. Don’t worry, the mat is hardy, and as long you don’t brush too hard, your coral will be fine.

Fish Or Critters Disturbing Them

If you have critters like hermit crabs in your tank, they can often disturb your corals by walking over them. While this should be temporary, if your colony has a lot of algae and detritus on it, they will be on top of the colony too much feeding on the algae. Use a turkey baster and blow off any dirt and old food, and you will need to clean it with a brush if algae is present.

You can also have fish that will constantly pick at it if algae is on it. It is a food source for some fish, so once you remove the problem, then the fish and crabs will stop picking at it.

High Salinity In Your Tank

This is an easy remedy because you should just be able to check your salinity. It should be between 1.020-1.026, and it needs to be as stable as possible.

You should be measuring your tank’s salinity with a proper refractometer. If you are using a float or another cheap measuring tool that you got from a big box fish store, then we recommend getting a proper tool. They are more accurate and not expensive. If you think you are having issues here, it is worth it to invest in a proper refractometer.

New And Acclimating

It is not uncommon for any new coral to get stressed when it is put into a new environment. It may open up in a few hours or it may take several days. The important thing to understand is that you need to not keep moving them around if they don’t open up immediately. Remember, these are living organisms that will react to their environment. You may receive a frag that has been established on a plug for awhile, or you may get a piece that was just freshly cut.

A green star polyp that was just cut from a larger colony may take a little while longer to open up again.

There are going to be some changes in water parameters, and it just may take some time for your GSP to acclimate. Again, give it time to adjust. Of course, at some point you will need to determine that your coral has had enough time to acclimate, and if it is still not open, then there is a problem that needs to be corrected. Hopefully, our article can provide some helpful solutions.

If your GSP frag is new to your aquarium, then it may take a little while to look right again.


Pests are a common reason why a coral can be acting up, and this is no different for green star polyps. Hopefully, when you acquired your coral frag, you dipped it. Of course, your coral may be established in your tank, and you may have introduced a pest onto it from something else.

You can visually inspect your coral to see if you can notice anything.

What Do Green Star Polyps Look Like When Closed

green star polyp that is closed

These corals look like a purple mat with bumps when they are not fully opened. It is easy to tell when they are shut. When opened, they look like whispy strands of green grass moving back and forth in the current under the water.

How To Get GSP To Open Back Up

green star polyp coral fully open

The first thing to do is to identify the cause or possible cause of the closing. The most common causes of a green star polyp not opening are placement and flow which are also directly related.

This will require you to adjust your powerhead or move your colony. The flow is either too light or too strong, and from our experience, it is usually not enough flow.

The key thing to remember is not to go crazy with too many adjustments, and it may take a week or two for the coral to adjust and open back up.


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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