You know, believe it or not, aggression really isn't a problem with my Cons. Yes they flair at each other, but no damage done. Even weirder is that they all have made their breeding ground on the same end of the tank. I started with just a male and a female. The other two pair are their brood, so really they are in breeding. But man, talk about some beautiful fish when they get "in the mood".you could do a small GT in a 40gal for a short time. Sounds like your 55 is WAY overstocked. How do you keep the aggresion down with 3 breeding pair in a 55?