Rotala macrandra var Narrow Leaf will grow in pretty much the same conditions as Rotala macrandra, Rotala wallichii, et al. Give them moderate NO3 (5-10ppm), high PO4 (1.5-2ppm), plenty of light, and plenty of iron (Flourish/TMG). They also seem to like water on the softer side (doesn't have to be SOFT, but not the more extreme GH 12-15+).
If Rotala magenta really does not work out, a more suitable replacement would be Ludwigia arcuata (as they have similar leaf texture and color) which is much easier to grow.
Carlos
If Rotala magenta really does not work out, a more suitable replacement would be Ludwigia arcuata (as they have similar leaf texture and color) which is much easier to grow.
Carlos