well i got mine to breed by switching to sand, you then could see them excavating the cave by spitting out the sand.
i then fed them on frozen daphnia for a week, and now i have 20 little kribs with the parents at about 6 weeks old. but now there gonna breed again as there doing the dance and both of them take turns going into the cave and spitting out the sand again.
but i must warn you when bred, they killed off two adult male kribs and a fully grown
rainbow cichlid