I am wanting to try again with daphnia, too.
Right now I have a 2.5 gallon tank that I use as a snail farm for my puffers. It has tons of ramshorns, a few neocardinas, and that's about it. Every few days I drop some algae wafers, maybe some Ken's veggie sticks, or some flake into the little tank and they snails are just exploding and sustained for months. I do a 90% water change 1x each month and that's it.
There's an assortment of live plants in there, and I always have some of them in a state of decay, to try and keep the water full of microbes and rotting plants, which seems to work. It actually stays incredibly clean in there!
I am starting to wonder what might happen if I were to just throw some daphnia in there. With nothing to eat them, I wonder if I coudld keep them going!
"The fewer our wants, the nearer we resemble the gods." — Socrates