Just wanted to chuck in my twopennyworth to this, for people's opinions... I had 4 angels in a 200 L tank and soon identified that they seemed to have paired up at opposite ends of the tank. (curiously, after a while they changed ends.... half time maybe?)
I had noticed aggression between two (it was like watching tag wrestling) so hoiked out the pair from one end of the tank and moved them into a small tank i use for ocasional breeding or nursery functions. Before you all rant up, it's only 20L size which really isn't suitable but there's no other fish in there, and the pair spawned a couple of weeks later so can't be that bad!!!
As luck would have it, this was the day before my holiday so I chose to remove the parents.... none of the eggs hatched without their care. A while later, they spawned again and after a couple of days I noticed the eggs had vanished. I quickly found though, that they had moved them to a different area of the small tank. Again no babies, but an improvement by leaving the parents in place.
In recent times I took the other pair of angels and placed them in a similar tank and e ventually they too spawned. Based on previous experience I left the parents in, but they got hungry after 3 days and ate the eggs. At feeding time I have noticed some short term aggression but generally peaceful, but tonight half hour after their feed, i saw them lip-locking. As far as I'm awar, angels pair for life and having spawned once, they shouldn't need to establish suitability of a partner....
Any comments?