Green star polyps are like beautiful weeds, it is pretty hard to hurt them with water parameters. If your parameters were bad enough to hurt them I am sure other stuff in your tank would be hurting/dead.
I had some "green" star polyps hitch hike into my tank on some live rock. The rock was bare when I got it and now a brown version is growing on them. I also bought some really green ones that had a fungus growing on them in the store and in my tank some snails jumped on it and ate the fungus and the green stars grew back over the spot in just a few weeks. Too bad there are not more color varieties
Plenums and ultra deep sand beds > all other setups!