Being only around 5"+ adult size I have used 50s, 60s, and 75 gal tanks.
The males can get pretty pushy in smaller tanks, and I like to keep them in harems of 3-4 females for each male.
The balzani are 2 males and 4 females in a 60 gal with some Uruguayan corys (C erhardti).
There is a larger group of Gymno quilero so last winter they were in a 125 with red ceibals and Uruguayan pike cichlids,

this year they are in a 500 gal kiddy pool in the basement with the above, plus overwintering koi and goldfish.