Well, I have hesitated to respond to this probably because I tend to get too detailed. I think the answer depends on the specifics of water, food and temperature. I find raising daphnia easy, like real easy indoors all year long. But it can be very frustrating. I still have an occasional unexpected die off which is why you should always have at least three cultures going or a good source of daphnia to restart.
I believe Pat has me scheduled to talk about raising live foods in January or February 2010. I will describe in fair detail methods to raise and harvest daphnia as well as microworms, grindal worms, vinegar eels, paramecium, and brine shrimp.
I have sold a lot of daphnia and hear many success stories and many who say they lost them all or the culture was doing well and then it disappeared. The only sure way to raise daphnia consistently is to start a culture and when it fails, start again and keep it up until you know what to do.
Overall the cost to raise daphnia are not much on the food since they will eat most anything. The easiest is green water if you have it, if not, fish food of any type. But you can feed most any mashed vegetable. And yeast out of the package is great. The key is how much you feed, since if you feed too little, the amount of daphnia tends to stays low. Too much food and the daphnia die. Just right and the population explodes. The real cost in raising daphnia is in your time but that can pay off in terms of getting your fish to spawn or to getting your fry to grow fast.
:lol::lol::lol::lol: