Hi Jim,
So when you say the pair where breeding, you mean they laid eggs, right? But none hatched? Or they ate them, or what happened? I like to keep my possible pairs in the group tank for the social interaction and competition, and let them work out the breeding pecking order. SOmetimes I've gotten lucky and the fry even hatch there, but of course don't last. Once they've paired up, then I move them to their own tank. Also works fro my limited space.