I actually just got rid of my red-tailed shark after having him for about 3 months cause as he got older he became VERY aggressive. He chased my fish all the time and eventually killed a few from the stress of them trying to run from him. I tried to make all kinds of hiding places for the other fish but he actually stalked them and sought them out! So no, i highly don't recommend you put a shark in with less aggressive fish, best suited to living with other aggressive fishies. I also had a 29g tank