I have Sun Corals in my tank they do require feeding to an extent I feed combination of food to my fish which includes cyclopes I've had them in my tank for several years and they've reproduced very successfully they are on most of my rock work underneath and in the dark I even have them growing on the back glass in caves. I have failed on them also I bought all yellow ones and they did great and I also bought some that were yellow with an orange oral disc that I got no polyp extension and eventually died. If you do buy them from your local fish store see if they'll feed them and hopefully you'll get polyp extension that would be one I would buy. I have bought ones that were closed up and actually never opened even when fed
The great thing about them is they don't take up any space in the light the bad thing about them is they open up fully in the dark so you don't get to enjoy the color so much couple pics are just some random ones growing that popped up out of nowhere