Plerogyra Bubble Corals get their name from their distinctive bubble tentacles that inflate with water. They have a slight translucent appearance and can grow to a very large size when provided optimal conditions. They are a fairly hardy large polyp stony coral and can be kept in mixed reefs as well as coral systems designed specially for LPS corals.
Bubble corals cannot be propagated easily in that cutting them is generally a bad idea with poor results. Having said that, they are one of the few LPS of this kind that recovers extremely well after a catastrophic die-off. Many times I see a dying Plerogyra almost completely vanish only to have little bits of flesh remain. Those remnants then quickly grow into small colonies and are very healthy. If you have a struggling bubble coral, it may be best to leave it alone and see if you have babies form later.