One of the best foods for Daphnia is greenwater. Greenwater seems to have tremendous ability to suck ammonia products out of the water, if given good light and was used by old-timers in hospital tanks. (Shelter + good quality water allowed fish to heal themselves.)

If you have the tank, set it up with gravel and on a good light, much like you would for plants. Put a bunch of fish in and forget the plants. ;)

Greenwater consists of all sort of microscopic critters already in your aquarium water. The additional fish waste and light simply encourage an explosion of Paramecium, Euglena and the like. They are mostly protists, not algae despite being called that. They are mobile and hunt for food, but also have chloroplasts. Hence with light and as their numbers increase, the water turns green.

Daphnia are opportunistic filter feeders. They can take everything from pea soup mix to bacteria to newly hatched baby brine shrimp and mosquitoes. They surely can take protists.

Some circulation is useful and helps the oxygen exchange at the water's surface - benefiting both the fish and greenwater creatures. I will use a couple of filters without the filter media (which would screen out the greenwater creatures). So the inside of a sponge filter can be dropped to a tank's bottom without the sponge or a small power filter, without any filter pads will work admirably this way. One could also just use a length of hard airline tubing.

The greenwater, under good lighting, can be very prolific. Half the greenwater from a tank can be removed and fed to Daphnia daily. I'm gradually adding water to an Endler's tank even now since 45% was taken out yesterday to feed the Daphnia and give a neighbor a 3-gallon starter culture.

Baker's yeast is also a very good Daphnia food, but a little must be sloshed around in very warm water and then cooled. One only feeds enough of that yeast solution to lightly tint the water. Nothing is fed until the water clears. If too much is fed, the oxygen is sucked out of the water and all the Daphnia suffocate. If one is patient, many times a Daphnia culture will regenerate from eggs left by the Daphnia (this also applied to periods after winters, summers and when the squirrel drowned in the barrel outside). Keep them pretty full so varmints don't drown.

Outside, a little well composted cattle manure, leaves that fall in, a very little of that fermented grass solution used to lure mosquitoes, greenwater and  many other organic items can be used to fuel a Daphnia culture. Those books and URLs recommended back when will give quite a list. Hopefully in a couple of years we will have a list in an AKA publication as well.

With all of that water added to the Daphnia culture, water will have to be removed. Just as water changes are very beneficial to fish, so too Daphnia thrive with changes. I often take a cut open gallon jug and dip out Daphnia and water. That is gently poured through a fine meshed net over the garden (or a bucket about to go to the garden.) The Daphnia in the net is either released back into the culture or save in a jar for feeding. It will go through a set of three or four sieves which have been placed in the opening of a widemouthed gallon pickle jar. It is lightly rinsed and each sieve is emptied into a smaller jar of clean, seasoned water. That of course is conveyed by turkey baster to the appropriately sized fish.

And a whole lot of greenwater is returned to thew culture. Small amounts are just poured in. Buckets are left on an old wooden stool and siphoned in.

E-mail me off list when you are ready for some Daphnia, this year or next at
unclescott at prodigy dot net

That silliness is done so BOTS don't put me on any more mailing lists. ;)

Oh! In case you run out of reading on the subject: