So I recently purchased a 55 gallon aquarium from a guy. Along with it came an adult Red Shoulder Severum (about 7-8 inches) and a Sailfin pleco (about 9 inches). I've been doing some reading about suitable tank mates, but I have some concerns with Severum being so old and large, and its possible aggression introducing new, and smaller fish to the tank. In the short time I've had it, my wife and daughter have grown quite attached to old "Fred" and I would feel guilty re-homing him so I could set my tank up the way that I want. Any advice on how/what to introduce, and if it's possible, would be appreciated.