prompter: Why is green star polyp coral not opening?
assistant: There are multiple reasons why a green start polyp coral does not open. Those are some of the reasons: 

1. Water flow

Green Star polyps don’t require high water flow but they will need low to medium flow rates. If they don’t receive the proper amount of water flow, they will stay closed up and not open. Too much flow can also cause their tentacles to stay retracted. They love water movement that is either pulsing or variable flow rates. Constant water flow that is too strong or pointed right on the coral will prevent them from opening.

2. Lighting

Another reason why Green Star polyps won’t open is due to lighting issues. These corals prefer a low to moderate light. High lighting will cause stress and they will not open properly. Make sure to position them in the tank where they receive low to moderate light. Some GSP corals will do well in shaded areas of the tank where the light is not directly pointing to them. GSP corals will also stay open if you use an actinic blue light at night.

3. Placement

Green Star polyps will be happy if you place them in the correct area of the tank. It’s best to keep them in the lower to middle sections of the tank where they will be out of the intense lighting and water flow. They love to be placed on top of the rocks.

As soon as you pick them up they will close up and become a purple mat until they are placed down and get comfortable again.

4. Change in parameters or temperature

Ideal water parameters for Green Star Polyps:

Salinity: 1.025
Temperature: 78-79F
Calcium: 400-450ppm
Alkalinity: 8-11 dkh
Magnesium: 1200-1350ppm
Phosphates: 0

Regardless if you are talking saltwater fish or corals, it’s important to maintain water parameters as stable as possible. Fluctuating parameters cause stress to livestock and it is easy to see when they are stressed. With green Star polyps, they will show this by not opening.

5. Acclimating them to a new tank environment

If you are introducing a new Green Star polyp coral into your tank, it is common for them not to open up for a period of time. They need some time to adjust to their new environment.

6. Critters are crawling in their copepods, snails, shrimp

It’s possible for certain invertebrates and other critters to crawl on GSP corals which can be stressful for them. It’s common for copepods to hang out in them as well.

7. The water changes, or the glass needs cleaning

Whenever you are performing regular maintenance on the tank-like water changes and cleaning the glass, it’s possible for GSP corals to close up.

When you are draining water from the tank you might notice if the hose or any piece of equipment is near the coral, they will close up and not open. 

8. Fish are nipping at the algae around them

You may have certain fish that like to nip at algae on rocks which can cause some stress to Green Star polyp corals that are placed on rocks. Fish like Yellow Tangs, Angels, Butterfly, all nip at algae on rocks.

If you have a Mandarin Dragonet Goby, they will eat copepods that can hang out in GSP corals. This will prevent the coral from opening up properly. They will stay closed until the fish stop nipping at the rocks. 

9. They are being fragged

Coral fragging is very stressful and it’s expected for them to not open up during fragging. 

10. The lights are off at night

Throughout the night while the lights are off, the Green Star polyps will remain closed until the lights are turned back on. Sometimes in the morning when there is some daylight in the room, GSP corals will start to open.

I hope that was helpful.
prompter: Please explain to me in detail what you mean by item 9. - What is fragging?
assistant: Fragging, in the context of corals, is short for fragmenting, which is a way to propagate corals by cutting them into pieces. During this process, corals spend most of their energy regrowing, so they might not open up until they are complete. This is probably not your issue, unless you acquired the green star polyps from someone who recently fragged them.