The first soft coral I ever bought was a "Colt" coral. It is listed on my 29g's webpage. Mushrooms, Xenia, button polyps, etc are all corals, but I don't look at them like that. The Colt coral was like a cactus, with a thick trunk and many stalks reaching upward, covered with thousands of little polyps for filter feeding.
It grew quite large in my 29g to the point that I thought I'd have to remove it. It spread onto another rock nearby, and I was able to take that piece and put it in to the 55g reef.
The parent colony was badly stung by red mushrooms last year, and never recovered. It just shrunk more and more, until it was removed. The other colony grew quite large and was very pretty.
About two months ago, I added a Red Goniopora to that tank, and put it right behind the colt. They rubbed against each other, but neither looked like they were in trouble and no slime developed. Great, right?
Unfortunately, it didn't work out and the colt began to shrink in size. At this point it is almost gone, dissolving away and falling apart. It is kind of sad to lose a coral that I've had for about 2 years, but in the big picture I have two beautiful reef tanks. Maybe later I'll get another Colt.