You haven't happened to have done a major water change have you?
It's a bug-bear of mine, but I find that in Toronto they are using Chloramine in the water which is lethal. If you're tank is only a month old, did you put all the Africans in at the same time. I did that once with similar results. The original foursome survived, while all the news one did not. I had put the new ones in all together hoping that there would be less agression by mixing it up. I was quite wrong. Slowly I have been adding fish, 1 or 3 a week and all now is well. What happened to the first bunch remains a mystery. Jeff
PS Does anyone know about the African Cichlid tank at the Toronto Zoo. It's literally stuffed to the gills with hundreds of Africans.