hey doggfather, I would wait to see what happens between the two. If the fin nipping is a territorial thing they can sometimes work it out after domination has been established. I'm not sure about the specifics of your tank but a few more angels might make the territorial issue easier because it spreads out the aggression instead of focusing on one "weaker" fish. If in your opinion the attacks are too brutal then I would seperate them. If you can't do more angels then make plenty of hiding spaces for the "weaker" fish, or a division in the middle with tall plants so the dominant fish has a more defined area for its territory.
On the other hand, if it's a breeding pair, I would still wait until the point the fish are actually breeding before the necessity of a new tank. This is because many fishes first spawns are unsuccessful or produce very little fry. So if you were to notice them having spawned then remove the eggs so they don't terrorize the tankmates, and after that then go ahead and get the other tank. If you want to try to artificially raise them, then do some research and go ahead and give it a try.
But if you notice the two becoming friendlier to each other (hanging out, cleaning at leaves or other smooth surfaces) you might have a pair, and could probably do another tank at that time. (Also, some pairs might not stay pairs after being moved.)
It's also nice just having an extra tank, but it really depends on if you can, or have too. Well, I hope this helps ( and if anybody sees any incorrect info let me know)
