If I had your type water, I'd keep them in a tank with an aragonite or crushed oyster shell substrate, or barring that possibility I'd run a fluidized bed filter, more as a reactor with aragonite as a buffer, or run a sump with sea shells or oyster shells under a water flow to act as a buffer.
View attachment 1508328
Below a DIY fluidized bed reactor using aragonite as media.
View attachment 1508329
Or....
I'd find a South American alternative, or...
If your tank is mixed geographically,
the African genus Pelviachromis is very similar appearing, soft water, lower pH alternative.
