Starfish problem

[Saltwater_Reefing]

I have a sand shifting star fish and like over night it has long a decent chunk out of it's leg, everything in the tank consists of 2 snowflake clowns, 1 yellow watchman goby, 1 pistol shrimp, 1 emerald crab and 11 snails. I feed the tank every other day and I feed this homemade food from a local fish store.

 

[AC1211]

Picture? Also I would guess either the crab or the shrimp is the culprit. Plus tank size? Sand sifting stars need a lot of food.