Just out of curiostiy clockwork what fish do you have in your tank
They can be, but in my experience when a fish in the cichlid world is less than half the size of a large aggressive cichlid they're often ignored or not as vigourously chased. The larger cichlid doesn't see the smaller cichlid as a threat. Meaning the little cichlid is no threat to mating rights or food source or even territories as in what can a small juvenile cichlid do to a large adult. Cichlids close in size fight for these things, but when there's such a large difference in size, it's obvious whose the alpha and whose gonna get his way. Also luckily most Vieja are vegetarians so the adult won't even look upon the juveniles as a potential food source. Plus Vieja have in general proportinitely small mouths for their size so they couldn't even eat the juveniles in the tank unless they were really small. Size though won't always stop aggression as even a small growing cichlid will often challenge larger cichlids for territories and such if both are adults. For instance if there was a mature convict cichlid in there it would probably be on. Lol! At least that's what I've experienced, I guess aclockworkorange will give you a more definitive answer in his case.I thought that Black Belts were really aggressive.
I was either going to get the Argentea or a Datnoid. I was leaning towards the Argentea though.