Daphnia are tiny crustaceans that may be collected using a plankton net or purchased from biological supply houses. In the alternative, you may start a culture by adding pond water and some dead leaves or hay to a jar or aquarium that is placed in a sunny location. The largest and most often available species, Daphnia magna, reaches a length of 0.25 inches and does best at temperatures of 75°F to 80°F (23.6° to 26.6°C). Most species of daphnia mature within one week, with adult females being capable of producing 100 or so eggs every few days. Daphnia can reproduce without the presence of males. Daphnia can be fed algae tablets and liquid foods sold for filter feeding invertebrates. They do best in aerated aquariums that support a growth of algae. Due to their small size, daphnia will be drawn into the intakes of most filters, so filtration is best achieved using live plants and algae, water changes, and possibly a sponge filter.
If you use pond water and bottom debris to establish your daphnia colony, check for the presence of the larvae of dragonflies and other predatory insects, and for pests such as fish lice.