I have a Sarcophyton that's about 12" in diameter, hate to think how big it would be if I hadn't trimmed it. I just take cuts around the outside, basically making the diameter smaller. The ring cut off is divided into smaler pieces to grow out. Doesn't affect the larger coral much at all. Just be careful about taking too much at once, mostly because all the pieces produce lots of mucous which can foul your prop tank (experience talking)