I leave my male and female BN in the same tank, mainly because I have other male BN's in my other tanks and adult males will not tolerate each other. Ideally the male should get a break between batches of fry. It takes a lot out of him standing guard over the eggs, gently swishing them with water, and then to guard the newly hatched fry while they still have their egg yolks attached and all this time the male either doesn't eat or only has tiny scraps of food. The female basically has a break while the male is busy doing his dotting dad duties, but the male wont really get one if always with a female.
If your wanting your BN to show his true fathering abilities then I would only have him with one female at a time, any more then that and I find he will get far to many eggs to tend for and they start getting knocked out of the nest hollow/ log. Plus females can be pretty darn territorial in BN society as well.
