Softer water does help. R. macrandra and magenta like more light then anyone would think is reasonable. You can try to rule the light out by letting one stem float for a week or so. If it starts to look good then you need more light for those guys. If you can, bumping up the co2 (slowly) and double-checking the circulation won't hurt either.
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They both like current, not a huge amount, but gentle swaying is good.