Hi,
I find that Daphnia breed esiest when left aone to their own divices.
i just put some cuttings into a water butt and some sludge from the pond.
thats it and let nature take its course.
but I am sure there are sites out there that talk about it and using leaf litter and getting the composition of the substrate right, for daphnia to breed, I also think tat a strong warm light source always plays a key factor as they use a form of photosynthesis using algae and phytoplankton.
google will give you more indepth descriptions of there natural habitat.