I've kept Gymno bazani "Bella Union", and don't think of them as a soft water species.
I kept mine in unheated tanks (room temp) in water between 7.5-7.8, alkalinity of @ 100ppm, nd a general hardness of 250ppm.
I used high altitude Mexican live bearers, and Uruguayan Corydorus erhardti as dithers (because they tolerate the cooler temps used for the Gymnos (68'F to 72, in summer low to mid 60s in winter). My group consisted of 2 males and 4 females.
For a while, other cichlids in the tank were Ciclasome dimmers "Uruguay".