Green star ploys are essentially indestructible. You just need to take care of the tank and it will do well. It will do OK when the rest of the coral struggle. So, how is the rest of your tank? GSP really need no special care.
That's funny I am trying to get mine to stop spreading, they got so bad they were growing up the back of my tank and on the overflow. Finally had to almost break tank down and spend hours scraping them off the rock. My advice is once they start to go isolate the rock they are on otherwise they will take over.
Those GSP also will win any coral war they encounter. It is wise to keep them isolate. I let it grow up a wall. Nice wall cover and easy to harvest. Slide it off near the top and peel off attached to a rock and sell to LFS. A carpet of GSP really pop under actinic or LED
don't listen to these guys. It does take a while before it encrusts the first bit... then it will spread. Like xenia, if you keep it cut... you'll be fine.