Why do so many people have it in for RTBS? I cant believe its just dumb luck I've had with their non-aggressiveness. In my experience they are purely territorial in agressivness, and less so than most cichlids. In a 20 gallon tank, what I consider to be bare minimum for them the are fine if given a hollow log or similar hide to call their territory, in anything less than a 20 they tend to treat the whole tank as theirs, above that size the tank is simply to big really for them bother patrolling constantly as long as a suitable "home" has been supplied.
Of the two tanks I currently have with Red tails, one is a 40 gallon with an adult and a 7+cm juvie. This tank also has cories and and a few other community fish, the only aggression shown is when the chases my large bristlenose or the juvie shark out of its log, chase ends as soon as the perpatrators are 4-5inches from log entrance, perp's may return to vacinity but are not hasseled as long as they dont seek to enter the log. I have never seen them show any aggression to my tetra's or cories.
My other tank with red tails is a 60 gallon, with two 9ish cm sharks and 7ish cm flying fox. These sharks have their own logs in this tank but are often seen cruising in formation (yes thats cruising NOT chasing). generally no agression is shown to the flying fox as long as it doesnt seek to enter the sharks percieved territory, there would be more aggression shown to the pair of kribs in the tank but thats probably beause there territories overlap slightly, the other tank mates are probably to big to bother with 6"pleco, large 3 spot gourami, a BGK and a young pair of convicts.
these are just some of my experience's with red tails which for some reason may be out of the ordinary, but I prefer to think its a case of a fish that is generally misunderstood. And yes I do intend once I have a good selection of adults and a suitable tank to attempt to try breeding them, a challenge I am patiently waiting for.
Andrew