Personally i would go to pundland or somewhere similar and get 1 of them cheap plastic containers, buy a cheap air pump, set it up and leave on windowsill for a week or 2, then buy the Daphnia or Cyclops and put them in the tank.
If the water doesnt turn green by the time you put them in, then put a small amount of actiavted yeast in, just enough for it to turn cloudy (i bought this from Sainsburys for like £1.60).
It will most liekly take a while to get a good culture going, iv had mine set up for about 2 months now and have a huge population but i made mistakes by overfeeding which made the water quality really bad.