I"ve always had the best luck with angels when I kept them by themselves in a species tank. Larger always seems to be better when it comes to tank size.... plus you can keep more! They seem to choose their mates, and just because you have 1 male and 1 female doesn't guarantee they will breed. I have had 3 pairs that have bred for me in the past, but I always had to artificially hatch the eggs, the parents would always eat them if I left them in the tank.