Green star polyps are fantastic and once they take hold they grow and spread very quickly. In my last tank I had one which grew so large it covered a huge piece of rock and then covered what must have been a third of the rear glass - it looked like a sheet of grass when they were all out - absolutely fantastic.

Personally I found that they do best with a medium amount of light and water movement, plus if you want them to grow faster keep your iodine levels up as they use this to lay down their mat.

Keep us up to date on your progress - interesting stuff.