err, natural as in stuff they find on the bottom without me putting it there directly; the bits and pieces of old food and whatever else is in the tank. Maybe natural's not the right word.
I did get some shrimp pellets, which the other fish were curious about but not enough to scarf them all up, so these guys should be OK.
As for frozen food, I have not tried that yet. Freeze-dried yes, frozen no. I suppose that's next.
All cwt posts are implicitly appended with "just my two cents".