Ken,
Sorry, I have not kept any one alive for 20 years, but I have a few that made 5 years. There is a website just on Goniopora husbandry.
http://www.goniopora.org/index.htm.
What always ended up killing them was moving the tank. They couldn't handle it.
One trick I learned that did help longevity was never, never touch the membrane with your bare hands, and spot feed them a mixed menu.
Ron Hunsicker (from north central PA. -- he used to have a fish store up there) discovered this trick and was very successful with them as well. Ron had a "blue thumb", he could grow anything in a reef tank. T
I took a trip up to his store, with Anthony Calfo and Mike Paletta, several years ago, we were amazed at his success.
He had several goniopora, some over a foot in diameter (with expanded tenticles).
I'll see if I can find the pictures and post them.
He had the biggest sarcophyton I've ever seen. It literally filled a 120 tank from top to bottom, and was about 2 feet wide at the top. They tried to move it to the Carnegie Science Center, but the move did too much damage, and didn't survive.
Doug