I also agree that having just one red tailed shark would be the best. I have 3 of them in a 55 Gal
. and even if it seems to be more than enough room for all of them they still peck and chase each other around the whole tank...pretty punchy bunch. I like to call them the 'terror squad'. There haven't been any casualties or major disturbances though. I've found them displaying this behaviour only towards their own kind (as newlywed had mentioned) and they barely take notice of other fish in the tank. In fact, they just go about doing their own thing (looks like a game of tag or something.) I have had a bunch of tetra in the tank they're in previously, and there weren't any problems...currently they're also with several plecos and there is never any interaction between the two species. Hope this helps and it works out.