Then you have had the opposite experience. I could not grow the Rotalas in Chicago tap water (GH ~13-14) for a very long, yet could always grow them in Miami's GH 5 tap water.
A few months ago, I began to add a 50/50% tap/RO mixture at water changes which has dropped my GH down to around 7. I am now having great success with all the Rotalas I had difficulty growing before in Chitown -- macrandra "Green", Nanjenshan, pusilla, sp. Goias, and rotundifolia "Green," etc. I haven't tried Rotala macrandra (red broad) in here again (have it emersed in Miami, actually), but the layout just doesn't call for it... but I am tempted.
Perhaps Ca/Mg relationship is the culprit and not actual hardness? Hmm.