Yellow polyps are one thing I do not have any luck with at all. Even those I get from my friend that routinely has to thin them out, he places them in a 10 gal with eclipse hood with little to no flow on them, and they look fine. I get them and put them in my tank and they look great for a day or so, and then just semi open up and set there. Have sufficieint current etc, and have played with placing them in various spots in regards to lighting, still they fail to thrive...within a month they are usually history.......