Lots and lots of phytoplankton!! Most generally find a dark spot in the tank and hunker down if they don't feel threatened
Phyto-feast is a good brand of phytoplankton. For feeding, add a squirt of this stuff daily to your tank slightly upstream of the scallop so it can be filtered by him.
These guys don't have too long of life spans (most not surpassing 4 years in the wild) and in the home aquarium, starvation is the leading cause of loss (usually after ~6 months)
Here's my electric! (This was the first day he was in my tank and has since moved spots)