Mine are doing really well on New Life Spectrum cichlid formula.
They aren't like many fish in that they don't usually rush up to the front for food (unless they're really hungry or in larger groups) and they don't usually swim to the surface either, it very much depends what they have learned to accept prior to your purchasing them - if they were raised on flakes and you feed pellets, it will take them time to recognize this as the new food source. It's my experience that they tend to see the food fall, casually make their way to it and then pick at it from the substrate, this is their preferred way of eating particularly with a fine sand substrate as they are then able to sift it...
Have you seen them pecking at the substrate at all?
What are you currently feeding them?
Blair.