Vieja can be unpredictable. I have had some over the years that played well with others, and I have had some that have attacked and killed other cichlids and even decent sized plecos. It seems like they begin to show aggression when they hit the size of your hybrids. With 73 of them, there are bound to be some "crazies" in the bunch.In 3 days, I assume the 73 Vieja hybrids killed 7 Burmese clouded archers overnight: