Decorator Crab vs Sand Sifting Star

I have a good question, I currently have a decorator crab. Will, the decorator crab try to eat my sand sifting star If I go and buy one. I need to buy something that will consume the detritus out of the sand bed...

 

Sand sifting stars don't eat detritus, they eat the critters in the sand and leftover food. Then they starve to death. Maybe try a tiger conch, which won't eat the detritus but will eat algae, leftover food, and bury itself to turn over the sand to keep it clean.