Given my experience, I would not use any filter at all. Daphnia need some circulation so their food will remain suspended in the water, but not a lot. Bigger bubbles are better than tiny ones, which might get caught under their shells and strand them at the surface where they'll starve.
Instead of filtration you just do water changes. Put a piece of very fine mesh, like panty hose, over the siphon tube, suck out a quarter of the water twice a week. Shake off any critters stuck to the screen on the siphon, then refill gently with new conditioned water.
Don't overfeed. Despite the fact they seem to thrive in algae filled ponds, tanks are an artificial environment. In a tank, too much food can literally use up the oxygen too fast and they'll die. Only enough food to last them a few days, no more. Once it is gone, add more. As the culture grows, more food at one time, but still be careful.
Baker's yeast dissolved in water first is a useful food, but remember, daphnia themselves have little food value. It is what they eat that gives them value, so feeding algae means they have a lot more to offer the prey animals they're fed too.
I've run across some great links on raising daphnia, moina and dero worms, if anyone wants them, just ask, I'll post them.
