More about the amazing powers of Daphnia...
I know of a spot in the vicinity of Death Valley, actually a trench in an abandoned mine workshop foundation, that has a sustained population of "annual" Daphnia. It only has water in this 6 foot long, one foot deep, one foot wide spot for about three weeks a year, and is in direct sunlight!
DEATH VALLEY!
Now that is some hardy eppiphia!
I use the "crash" culture method quite often to store mine long term often. I find letting the tank/bucket/tub dry out in direct sunlight after all visible movement in the tank has ceased works best. I have also found that glass containers (I use five and ten gallon fish tanks) are best. I suspect that even FDA approved plastics can leach out some Daphnia harmful chemicals over time.
And yes, I have had great luck with plain old live baker's yeast.. I mix up a few tablespoons worth with some water direct from the daphnia culture until it makes a runny suspension that looks kind of like skim milk. Then about once a day, I shake the mixture up really well and I feed about 20mL per gallon by squirting it directly into the tank in such a way as to get good dispersion. Its actually pretty neat to see those little buggers filter the water out clear in a matter of hours! You will know if you are adding too much yeast solution if you get a white goo on the bottom of the tank.
Advantages: Cheap
Easy, year round availability
excellent "bang for your buck"
a little bit of yeast goes a long way
Crashed cultures restart easily after a few weeks drying period.
Disadvantages: Yeast solution must be kept refrigerated
Yeast solution stinks like...well...yeast
Takes a bit of trial and error to get it right (in other words, always have more than one culture going at any one time, staggered out a few weeks apart in rotation)
Its easy to overfeed and WILL crash your culture after a few weeks.
Once you use a container for yeast fed daphnia, I do not recommend using it for anything but that.
Also, I am not sure of your budget or set up, but those HUGE 1 gallon pickle jars make great daphnia culture units and you can often get them for FREE if you ask around at a few mom N pop restaurants. (Unless you can eat a gallon worth of giant dill pickles in a hurry...)
Also, neat trick for harvesting Daphnia: Place a bright light over the culture for about 10 minutes, the daphnia will swim to the light just like brineshrimp, and can be scooped out with a wet brine shrimp net, or some old pantyhose streched over a bit of coat hanger...