Male Kribensis and Firemouth Fighting?

I have a 3 inch Firemouth Cichlid with a pair of Kribs, some dither Buenos Aires Tetras, and a 3 inch EBJD (Grow out tank) in a 29 gallon tank. Anyway, long story short, everybody gets along EXCEPT the Firemouth and the Male Krib. I don't understand why this is, since they have much different established territories. The Jack Dempsey and Firemouth even get along very well, but the Krib constantly bickers with the Firemouth! What do I need to do? I could move the pair of Kribs to a 10 gallon by themselves, but is that too small?