How is the rotala magenta doing? I came to the conclusion that I can't grow the rotala macrandra in my tank. I don't quite know what to think as the rotala magenta became very stunted on the new growth and started to get some hair algae on it so it became compost before it spread to anything else. The rotala macrandra that I have planted twice looked really good for a few weeks then it started to melt from the bottom up. I have been thinking about a plant to put in the place of the rotala and everytime I look at your tank the Patanal stands out so that is the plant that I need to find now.
dont give up. i had the same issue. but now in the same setup but with more CO2, i have r. macrandra variegated doing quite nicely, and r. macrandra green doing well too.
try planting a stem of it right between your foreground and midground. it wont look nice, but thats where the water is least likely to stagnant IME, and thus CO2 should be the most available as fresh CO2 rich water from the diffuser constantly washes over the leaves. if it does fine there, then you know what your issue is.