If sleeper gobies have a problem eating, try placing a pellet food like Hakarii, in various places in the sand. It sometimes gets them eating prepared foods. Once started they eat anything. Mine were pigs.
Its doubtful that any of our sandbeds can sustain sifters of any type for long periods, unless replaced by more live sand. They will deplete it in no time. The sand sifting stars seem to be the worse, as they eat nothing else. They will eat all the fauna in the sandbed and then slowly perish, or at least thats what the "experts" say in their writings.
Most of them, {the ones that write all the sandbed articles}, are against the use of sand sifting animals, because of the depletion of the critters in the bed, that are required to keep it a "live sandbed".
just thought I would add this post for whatever its worth.
I always liked my sleeper gobies, back when I had a dsb.