Notice that Orbitorly lives in Palmetto FL, on a limestone aquifer (right, Orbitorly?). If you insist on keeping Mollies in an unsalted tank, they will do well enough if there's plenty of calcium and magnesium in the water. The pH should stand naturally above 7.6 or so
If you want a dark fish in a planted tank I'd go for a solo Paradisefish, the darker the better.