I have an empty one gallon as well, where do you get daphnia? None of the fish store's in my area sell live food (except feeder fish). One sold brine shrimp but he stopped because he has to drive to miami to get them and with gas prices he was loosing money on them.
There are loads of them on aquabid. I was planning on getting mine from there (once I check to make sure my LFS doesn't have any starter cultures)/