6x2x2 minimum id say for a nice happy pair ,ive got mine in a 6x1.5x1.5 atm but they are moving to a 6x2x2 in a month roughly and from there they are getting a huge pond in the next year or two
125 is minimum 180 is overkill. Hell you can have a pair and about 3 other large fish in a 180 IMO. My Jag pair isn't aggressive though only to each other. Mine are happily housed in a 125. 125's are cheap very nice and have great footprints.