echoing what bill said, it's really hard to take are of Goniopora.The key to keep it long is to split it every few months.
What happen is the part of Goniopora that can't get light or whatever dies, then slowly everything gonna die. If you split it every few months, you won't have the problem..
The reason why red is easier is because the polyps tend to be smaller, so most likely all the polyps are able to get the light..