My experience has been to the contrary as far as low GH goes. Until recently I had no luck growing Rotala macrandra or Rotala magenta. The new growth tips always stunt and the small new leaves are twisted. Even though my tap GH=8, I thought I might try more Ca just in case because the symptoms do look like calcium deficiency. Well, after a month of CaCl2 addition (GH to 13), my rotala macrandra is drop dead gorgeous, blood red, growing/branching like crazy. Rotala magenta is doing much better as well.tsunami said: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.