That is a very interesting question. I have had two separate experiences with keeping more than one RTBS but both turned out much the same. My first was with a 29g. I had two of them and they chased each other sometimes and stayed on separate sides of the tank other times. But they never hurt each other other than a fin nip here and there. They actually, at times really seemed to like each others company - I think they were male and female.
Now with the 180g, they are territorial under certain conditions. I used to have SAE's with one RTBS, who is now 6 years old. The RTBS only chased the SAE's. Then I found an old ornament which is about 8"X6"X6". I put it in the center of tank toward the front, thinking I will have to move some plants around so I can place it properly later. But an amazing thing happened. It was just enough of a barrier to make the RTBS stop chasing the SAE. After I moved the ornament to a spot of my liking (more to the back and side), the chasing began again. This does not answer your question, but I thought it was worth mentioning. I did eventually get my lone RTBS 2 friends - I was hesitant on how he would react but, what the heck - I love to experiment. It has been over a year and they all get along fine. They chase each other all the time, never hurting each other. And they never hide from each other in the plants, the way the SAE's did. They also chase all the other fish if they get in their way (territory thing). Again, the other fish have not suffered any physical damage. And there are so many for them to pick on that not any single fish gets exhausted or stressed out.
So, I would say... try it. Try moving things around in the tank in case they do get rowdy and see if that calms them down.
I am sure that there are cases of extreme aggressiveness but in my case I have no problems. Good luck - cheers back to you!!
