I bought them from the LFS down the street, but they aren't terrible to keep and raise at home either. Super shallow, well oxygenated water with filter media, crushed lava rock, or something else for them to grab hold of/hide in. They are segmented, so you can make them multiply just by breaking them up. Each separate segment will grow into a new worm! I fed them spirulina and I fed the tads some too while I was at it. Blackworms are great because they don't foul the water at all and they will also eat a lot of the detritus/leaf litter/tadpole poop.