Well, for one, why have copepods in your fuge if they can't get into the main DT?
That's where you want them to end up to feed critters like mandarin's etc. Some people say they can't survive the trip through the pump.... I don't believe that. I think most survive the trip just fine.
As for filter socks, yup, they catch the pods. I spend probably 15 min per sock when I'm changing them out catching the little buggers and putting them back into the fuge, lol.