Unfortunately Cyprichromis just do not do well unless they are in larger groups. Their territory is virtual and it is huge considering the size of the fish. Males can be so brutal to each other and females. I am sorry that anyone would even sell a "pair", since they don't pair off, or have any bonding to speak of. The only way to relieve this tension is to separate them or get more. I really think you should have a minimum of 12 and a 90 - 100 gal tank, that is 6' long. Some people do try to keep them in smaller quarters, 4' 55 gal tanks, and while it s not impossible, it is definitely harder, and very often after time you end up with one fish.
So while Cyps are really neat and fun to work with, it is going to be easier with a large tank and a larger group!
Glad to hear your other cichlids are all doing well!