I have found most Vieja are non-agressive with smaller tank mates, but as soon as you put 2 non-mated adult, similar sized cichlids with Viejas, especially only 2, in a small tank (under 200+ gallons) there is a problem.
I had a 6-7" V regani in a 150 gal get very aggressive, so I gave it to a friend, who put it in his 225 gal, it killed a much larger 10" H. carpintus, then went to work on, and killed a very large (@12") Amphilophus labiatus.
I also had the same type situation with an argentea, it was very mild mannered until it hit about 7", first wiping out all other Viejas, then killed a managuense, and dovii.
The only time they generally work for me, is if the tank is in the 300 and up gallon range.
Because alone after killing all tankmates, the regani would spend all day hiding, my friend ate him.
I had a 6-7" V regani in a 150 gal get very aggressive, so I gave it to a friend, who put it in his 225 gal, it killed a much larger 10" H. carpintus, then went to work on, and killed a very large (@12") Amphilophus labiatus.
I also had the same type situation with an argentea, it was very mild mannered until it hit about 7", first wiping out all other Viejas, then killed a managuense, and dovii.
The only time they generally work for me, is if the tank is in the 300 and up gallon range.
Because alone after killing all tankmates, the regani would spend all day hiding, my friend ate him.