Wow… you guys can get pretty wild around here… looks real bad to a new guy on the forum 
I’ve kept an ESTABLISHED pair of adult JDs in a 55 gal ‘long term’ with no problems more than once…
I’ve introduced a male and a female (potential pair) to each other with a couple subdominant female tank mates of other species… and female killed the male… this was in a 4x2x2 120 gal…
I added several JDs to a 300 Gal Rubbermaid and the two pairs that formed both fought very hard, lip locking and tearing up fins… but once the pair formed and spawned, the aggression died down drastically.
It’s been my experience that regardless of tank size, the female wants to pair off with a male that is tougher than her. The females tend to fight hard against the male and force the male to ‘take control’ of the situation without killing her.
I confess I didn’t read all 4 pages of conversation, but I’m a Jack Dempsey fanatic and could resist sharing…
I’ve kept an ESTABLISHED pair of adult JDs in a 55 gal ‘long term’ with no problems more than once…
I’ve introduced a male and a female (potential pair) to each other with a couple subdominant female tank mates of other species… and female killed the male… this was in a 4x2x2 120 gal…
I added several JDs to a 300 Gal Rubbermaid and the two pairs that formed both fought very hard, lip locking and tearing up fins… but once the pair formed and spawned, the aggression died down drastically.
It’s been my experience that regardless of tank size, the female wants to pair off with a male that is tougher than her. The females tend to fight hard against the male and force the male to ‘take control’ of the situation without killing her.
I confess I didn’t read all 4 pages of conversation, but I’m a Jack Dempsey fanatic and could resist sharing…
. The 75 is 18" front to back that is where you get your extra footprint from. I'm just trying to say that maybe you shouldn't be so hostile to an opinion you don't like. If you would calm down and think about it actually is a very good point. Sure I agree a 55 should be big enough to breed JD's but a 75 would be the ideal tank size and would help lessen aggression that sounded to be getting pretty bad in your tank.