I've heard loaches can and will slaughter shrimp. Your results will vary with Corys since they are peaceful but can fit babies in their mouth.
I dealt with my planaria by getting a feeding dish, cutting back on feeding and getting some CPDs since I have a taller tank and they would inhabit the middle. I also got a Nerite snail to cleanup leftover detritus and not reproduce.
Those things are gross, man. >_<