sand sifting goby

Busted, caught this guy eating a hermit didnt see him picking on him or anything, anyone have trouble with their sifting gobies eating their CUC

So I was wondering, what should I get next fish wise. I have a 13 gallon with a pair of clowns and a cleaner shrimp + a clean up crew. I want to get a Exquisite Firefish, as my centerpiece fish. But I also want something that is productive for the fish tank like a sand sifting goby. What do you...