I have all of my springtail cultures on charcoal. This works because there is a lot of surface area for them to breed. I feed them rice. I have heard that some feed their cultures nutritional yeast, but rice works for me. Also, I do not feed my springtails to my animals, so they don't need extra "gumption", I just use mine as cleanup crew. Some also keep their springtail cultures on leca (clayballs), clay substrate, or just plain old ABG mix.