If you give them the conditions that they need they eventually should spread. However, that involves not only water quality, but other factors like lighting, the amount of water flow they're in, etc. The first coral I bought was a rock with about five mushrooms on it. From the minute I put it in my reef it didn't do well. They were shrunken and looked like they were about to die. And, that's despite that all the other corals in the tank thrived and grew and spread. Finally, after almost a year and a half, not contemporaneous with any changes in it's setting, the mushrooms picked up and displayed and now there are more mushrooms on it.