I've had an Orange Cactus Sponge for close to two years. It has been a challenge for me from day one ! It was a "cyano-magnet" for a long time. It has shown color improvement and cleaned itself up since I found the right location in the tank for it. Unfortunately that is a dark recess where it is hardly visible.
It has never grown.
Exposure to air will destroy their tissue as Mitch stated.