Scavengers mean 'carrion-eaters', not 'gunk/silt eaters'...
It needs to eat meaty food items, what fish could not catch. Don't starve it - if your fish eat everything you give them and nothing is left for bottom feeders than you need to feed some more for shrimps... Make sure it sinks fast.
I have tested the sinking pellets called 'crab cusine' with good results:
http://www.hikariusa.com/crab_cuisine.htm This is dedicated diet composition for crustaceans like shrimps. My larger shrimps will have a pellet per bite, I feed about 2-3 pellets per shrimp 3-4 times a week - smaller ones will munch one piece as their whole meal... hiding from competition of other shrimps. They are huge fun to watch. Enjoy!