Do you have any pics of the entire tank? Are all plants doing poorly, or just the Macranda?
Is your primary focus on plants or the Discus? What's best for one may not be for the other.
In general, Rotala Macranda's should be pretty easy to keep. Looks like you have decent light and CO2. I assume with Discus you must stay on top of tank maintenance.
My first guess would the CSM+B if that is what you are dosing. I would try cutting it way back and see how the Macranda responds. If it improves, I would look into alternatives for micros (DIY custom preferred).
And I noticed your said you dose 4.5 ppm P per week, but the reading at the end of the week is 1.0 ppm. What is your substrate?
As to macros, my experience has been that Macranda's prefer richer dosing than other Rotalas. I have a heavy fish load, but also dose NO3 and PO4, as fish waste has never been enough to keep these species happy. So my second thought would be to increase NO3 and PO4 dosing and see what happens.
But to me, the issue with your tank is the Discus. They are more sensitive to NO3 than most, so I would consult with other Discus keepers as to how they combine Discus/Plants.
Here is my Macranda from this afternoon. High light, high CO2, inert substrate, custom micros, and fairly rich macro dosing. Like I said, should be a fairly easy one to keep happy.