I've kept R. macrandra in all types of substrates: Aquasoil, Eco-Complete, Flourite, quartz sand, and even Caribsea's KH-buffered Cichlid Sand. In the harder substrates (Cichlid Sand, Eco-Complete) I noticed a higher tendency for the stems to melt although those stems that did not melt seemed to do fine going forward. I've had the best luck with Aquasoil and quartz sand, possibly because of their neutral to acidic makeup. I've also had better luck using good to possibly excessive lighting.