WYSIWYG* Mushroom is on a 1” frag for size reference. 
This Discosoma species prefer lower light than most mushrooms (PAR 50-100) as well as lower flow. These can detach if irritated or stressed. If this happens place in a low flow area with rubble to help reattach.  This one has been in our tanks for a few years and has been aquacultured under aqua illumination LEDs.