I am willing to entertain anything as a reason. I am not a scientist, nor was this a very thourough observation to draw any conclusion from. But (I keep repeating this) it is a fact that 1) they were fighting all day long, every day. There was literally no chance you'd walk in the room when they weren't fighting (unless the lights were off) 2) When I removed the background the fighting absolutely, immediatly, and completely stopped. There was literally no chance you'd walk in, sit in, or hang out in front of the tank for hours and see even a nod from either fish. Having given you this information, I will conclude that this was months ago, and the aggression has started rearing its head again. The cease fire agreament lasted 2 - 3 months without out one incedent. It has occured to me to buy a new dark background and put it on and see what that does. This might answer the question of wheather or not the simple change of sceanery had anything to do with it. However, they have never resumed to an all out battle where it was when I removed the dark background in the first place. There are many people who have responded to this post that said they've tried this with little or no results. And some have agreed with what occured in my tank. I conclude by this rather lengthy, long standing post, that there are no gaurantees. But I will say. Since I've removed my dark background, it has been a completely different environment.