IMO these do not last very long. Both me and a friend bought them on sale at a lfs, they were the electric kind. We I tried supplementing with marine snow and my friend used DT Phytoplankton (live, refridgerated) after a few weeks ours both died. We asked the store and they said that even they have difficulty keeping them, hence the sale. Maybe we got them and they were a bad bunch
If you do get them, they need some kid of specialized care and feeding that I have not figured out. Maybe someone else can chime in with their success.