I've definately watched my enchinata growing on my sandbed, it builds a skelaton for itself. My acan lords are pretty slow growers it's hard to tell in my tank.
Both species mentioned here of Acanthastrea will grow faster if placed on a solid substrate. A. lordhowensis will grow extremely slow (in comparison), if on sand.
Thanks for the input guys. The reason why i'm asking is because i want to put my frags on the sand but i needed to know if i gotta glue them to some rock in order to grow first. I was hoping i didn't have to glue them to rock in order to grow.
You can glue it to a larger piece of frag or rubble rock and then put that in the sand. Mine is setup in a similar way and it is growing like wild fire in my sand. When I moved it higher up it started to lighten up and loose color.
This is my acan when I first got it all beat up and dying. I had it in a 55 under PC's up real high. This was around a year or so ago
The second is when I first upgraded to my 72 with mH about 8 months ago. I had it up high for a while, but it started bleaching out so I moved it down low.