As Rocksor stated, neither normal JDs nor managuense are black water species, both come from the hard, alkaline rivers and Cenotes of Mexico and Central America. Black water might do the oscar good, but not the Central Americans.
Below is an example of carpintus "chairel", they would do well in hard, pH 8 water. Whether or not they will be compatible with the others may be another story, in a 75 I doubt it. The terms "escondido, Chairel, or Rio Hondo" are ancestral catch locations, the names of Lagoons, or particular areas.