mine is fine in the sandbed. I actually just swapped the position of my pipe organ with it and it is still doing great on the rock. I would move the zoas because when fully extended it gets pretty big.
I went to a lfs today, they always had success with goniapora over the years. I know this for a fact. Anyway last year late summer they got some and i was in awe today to see how much they grew accompanied with xenias. Some double in size. I asked the guy what they feed, he said they don't feed they dose alk/cal and add Kent Coral Vite occsionally. I got my chance afew years ago with a red Goni. some say the red ones are more hardy, it didn't make it although i fed it. Xenias don't thrive in my tank either. I don't think i'll be getting another Goni. any time soon maybe when i figure out how to crack the Xenia puzzle. For now i'll leave Goni. in the store.
My green and tan goni seemed to be more hardy than my red. But you can feed them. Mine love the coral smoothie. Another thing that might help is to shut off your protein skimmer once and a while. I got goni on the top of my rock and some on my sand bed. All opened up great.