It is not reccomended to keep a parachromis species with another unless the tank is very large. You may want to look into although you could look into getting your jag a mate!
I'd go with a mate for the Mana you have. Much better viewing the spawning rituals of a pair then watching to seperate species tear one and other apart over territory.
if the 125 is 6' long, than i'd say you'd have fair game with anything other than dovii, loselli's, freddy's, mota's or another jaguar should be fine with it. but you never know, it may work or may not, you have to try it though.
GOOD LUCK parachromis are outrageously conspecific aggressive IME. However, If you are going to attempt to keep another parachromis - you should definetly experiment now before he's any older!