When you do have a spawn in a community tank, retrieving the fry can be quite an ordeal. Completely dismantling a tank to catch a holding female is alot of work. Not to mention how traumatic it must be for her to be chased around a 100 gallon tank with a mouthful of eggs. When you have a breeding group in a tank by themselves, it is much easier to observe the females and see who is holding. Then they can easily be removed to a female holding tank, or stripped.
Aggression is less when each species is housed by themselves.
When you have three or four different species trying to spawn in a community tank, you are going to loose fish. It is just natural that they want to eliminate any and all other males in their territory. When bred one on one, much of the aggression is taken out on the female, but in a breeding group, this doesn't happen, he is too busy trying to multiply with all the females. Housing The larger the tank the larger your breeding group can be. 4' X 2' X 1' this has proved to be a good size.