if your looking for copepods the easiest way to recognize them is if you think of an amphipod as a dot the copepod is a speck, teeny little buggers.
and mandarins are quite the voracious predator (believe it or not) they will eat anything the can spot that will fit in their mouths that is alive and not wiley enough to get away. the hard part is (usually) getting them to eat dead food, or our prepared foods. its amazing how fast a mandarin can strip a tank of its population of pods, which is why for many years the rule has been larger established tanks rather than smaller tanks. so the population of pods is both large enough to sustain constant predation and resilient enough to out breed the non-stop eater that mandarin are. and they dont (stop eating that is) unless its sleeping a mandarin is generally on the search for its next micro-morsel of food.