I agree with everything Steve C has said. This is my third time with frontosas. As I wanted breeding I have always had them in a species only tank. They are usually docile but here is what happened to me.
I bought 3F 2M WC Mpimbwes over 2 and a half years ago. The females seem to spawn every 3 months, sometimes holding to term, sometimes not.
Problem was the last time one spawned, the day after, the alpha male (10 in) beat up on the smaller male (8 in) so bad I thought he was dead (but I nursed him back to health in an isolation tank). They had gotten along fine until that day.
Three times, at two week intervals I had tried to reintroduce the beta male. Within 10 minutes he was bitten and attacked by the alpha male. So removed the smaller male again.
This male was not happy in isolation and not happy getting picked on. The alpha male and three females are getting along just fine. I just had to sell the smaller male and get on with life.
Her is a picture of my alpha male and a holding female.