Ark, how often are you changing water? The plants need some poop left (nitrates). This is probably going to sound crazy to you (and everyone for that matter) but, as you know I do daily water changes on my juvie discus tank. I do not vac at the base of any of the plants. What ever poop is at their bottoms, I don't disturb, I leave. This seems to be enough ferts for my low light plants to thrive. I have swords, crypts, anubias, java fern, a dwarf lily, and frogbit in that tank. I do not have it heavily planted, just spot planted and let them fill themselves in. I have 1.5 wpg on the tank and dose nothing. I have 3 nerite snails and 11 amano shrimp for algae that may appear. Which isn't too much....a little green spot on the back wall and a little bba on the edges of a few sword leaves.
If you want some plants in your tank, that is the way I would go. You are right, it needs to be a discus tank with some plants in it.