Oh, regarding why some coral don't do so well in an aquarium. There are several considerations:
1. When one or two types of coral dominate the tank, their territorial toxins(allelopathic chemicals) inhibit and in sufficient concentration will slowly kill other coral/animals.
2. Activated Carbon adsorbs toxins. Place it loosely in a media bag in an area of good flow, like next to the main pump intake screen, readjust/flip the bag over weekly and replace it monthly.
3. Water changes help dilute territorial toxins. 10% monthly water changes are typically sufficient.
4. After Salinity and Temperature, Alk(Alkalinity), Ca(Calcium), and Mg(Magnesium) are the three most important components of healthy seawater. Testing these and keeping them within range are critical to coral health. It's part of the fun of reefkeeping to do these chemistry things.
5. Sometimes, after all is said and done, an individual coral or a species of coral may just not do well in a particular tank where everything else is doing fine. Xenia is one of these that grows like a weed in some tanks but disappears when placed in another tank.
Aloha,
Mark
P.S.
Of course, Butterflyfish eat some types of coral and beneficial worms so we might see a hobbyist buy coral to feed the Butterfly.
Edited by Mark Peterson - September 19 2015 at 9:28am