i feed mine peas, the frozen kind. i thaw them, as i put them in i deshell them and squash them in my fingers. i put in about 30 peas for 20 medium sized mbuna and with in 30mins they are all gone.
if yours dont want peas try going to a chinese shop and buying the unsalted seaweed sheets. my cichlids as well as my silver dollars and tinfoils go ape for it, and its cheap.