how can you get a daphnia culture started.
you can start by getting a 5-gallon bucket, drill some small holes 5 centimeters under the top of the bucket to work as an overflow, in case you feel like you need it drill another hole for an air line and air pump, and fill it with water, to that water you add some organic matter like cow manure, fish poop from the filter cleaning, dead plants, etc., and wait.
what you are looking for is green dust algae and brown algae and for chlorella and phytoplankton in the water column (aka green water), once that happens you can go catch your daphnia and add it (inspect it first to prevent dragonflies), now your daphnias biggest competitor and your worst nightmare will be mosquitoes so if your bucket has a lid, cut the middle of it just leaving the rim and glue a fine mosquito mesh, that will prevent them from laying their eggs, and the larvae that may have come with your daphnia from biting you once they mature.
this would be the prime time to use your invertebrate safe anti-parasitic medicine, always use it as the manufacturer says, check every week at the bottom of your tank for more dragonfly larvae and remove them.
now if you place your bucket outside make sure it will be in a place where it can get at least 4 hours of sunlight per day, some wind and rain in case it rains, this will cover temperature, algae blooms, oxygenation, and nutrients during the rainy season since rain water contained nitrogen and carbon dioxide which the algae will use to flourish.
every time you do your water changes re-fill the evaporated water from your daphnia colony with the water change water and if you see the water gain visibility then add more organic matter since that means your algae is receding because of a lack of food.
with this, you should be able to breed some daphnia.