i have no experience with these so this is just what iv read from others and iv seen lots of people post pics of their argentea pair with dividers in saying that unless theyr breeding they cant be together or he beats her up, maybe a pair where the female is alot smaller could be easier as you could provide hiding spaces that only she fits into so the male cant get to her, this could work with festae though
the males grow to like 20in so that would be pretty big as he would grow longer than your tank is wide, im growing some festae fry right now but will only be keeping a female in my 5ft 120g tank with tankmates because i try to keep fish that dont grow longer than tank is wide, but ive seen their parents personally and they are quite a sight to see