I know the red tail black shark will chase other around till no end but I have never heard of a problem with balas. Is the size of school of balas enough to over power the rtbs for bugging them?
Well I know many people who have been successful in keeping both Bala and RTB Sharks together. The key is to have a very LARGE tank, a place for the RTB to hide, and having at least two or three Balas. I don't recommend keeping more than one rtb as they don't tolerate eachother and/or similar looking fish.