With 20 shrimp in a well-cycled tank, I would recommend feeding much less than once a day unless you monitor exactly where the food goes and vacuum it up shortly after. For instance, I have a colony of ~80 in a 20L. I feed about the equivalent of two algae tablets a week, and have a bristlenose pleco in the tank to clean up the leftovers.
Cherry shrimp are hardy, but can sometimes be very fickle when it comes to breeding.
Cherry shrimp are hardy, but can sometimes be very fickle when it comes to breeding.