Daphina and RCS

You don't want them to be in a constant greenwater though. You use the green water to feed them. Like many other things, you can over feed them actually.
I culture daphnia, and this should work. I'd be more concerned for the RCS than the daphnia, as a very popular food for daphnia is yeast. I'm not sure if RCS can handle yeast directly.
If you get a starter culture, you'll want to float the bag first, and acclimate them the same was as any other animal. Then, scoop them out after and place them into the rcs tank. Feeding them every so often (once or twice a day).
They reprodce like crazy though, as the females are asexual. They are very sensitive to low oxygen levels and ammonia too. If the habitat they live in is not suitable for them, they will create dormant eggs, once that do not hatch and just float at the waters surface (they look like little black poppy seeds).
If the population crashes, there usually is no way of it recovering, so it's best to keep two seperate cultures going.
I keep daph in a bee shrimp nano tank (as back up daph incase of a crash), and in a big big bucket outside.
Spirulina wafers are fine as a food too. Drop in one or two for your rcs, but also, in a little clean yoghurt container, throw one or two in and add some water. Let it sit for an hour or so so its soft and mush and crush it up with a spoon or something so it clouds the water. Using an eye dropper or syringe, add it into the tank accordingly.
Usually, when feeding yeast, you want the water to be all murky and stuff, but not cloudy. Enough that its murky but you can still see through it. Do not feed again untill the water is completely clear.
Don't use a power or HOB filter, and if you use a sponge, watch it at first as sometimes the sponges are too strong and you'll see daph being sucked up against the sponge.

Hope this helps.