Sorry, Discus are not that sensitive nor is there any need, requirement or otherwise to keep NO3 at or near zero.
NO3 derived from fish food, and waste is quite another matter, as every bit will start off as NH4, not directly to NO3.
So keeping discus in planted tanks, as we add KNO3 for a nitrogen source, presents no issue/s.
As far as feeding them, more frequency is better than all at once(most common issue for most folks), also, some decent surface current, low pressure high flow movement in the rear of the tank is very wise.
Also feed a wide variety of foods, do not get stuck just feeding live worms.
If larger and faster fish from fry are the goal, consider a grow out tank (eg bare bottom) that's easier to deal with. If they are just pets and you do not need max size and brood, then you do not worry so much about it.
I bred some in a 90 Gal several times back in the 1990's feeding live brine and frozen foods in a fully planted tank.
NO3's where about 20ppm the entire time.
Plenty for plants.
I still did large water changes, typically 2x a week 50% etc, you can likely get away with fewer, but 2x a week is a good routine for most Discus folks with addition of KNO3, KH2PO4 and traces, with a little GH for color. No KH is needed, some folks have high KH, which is more an issue than GH.
The water change removes the fish waste, not the NO3.
We add the KNO3 back afterwards. The water change keeps any NO3 from building up and adding KNO3 keeps the NO3 from getting too low for plants.
The same applies to the dosing of the other nutrients.
Very simple and no need to test the water.
Do the water change and dose.
GH is a nutrient for plants(Ca and Mg), KH is not unless there's not enough CO2, then some plants might try and use the KH as a carbon source.
I'm not sure why folks still suggest that planted tanks and discus do not go together or that all NO3 is the same when they can come from very different sources and have very very different toxicities.
This has been going on for at least 15 years now.
The goal is not max brood and max size of the discus.
This is
not an industrial feedlot farm where we are trying to get max yields.
For breeders over on many discus sites?
It is for them
If that is your goal, then lots of food, frequency and water changes with bare bottom tanks will achieve that.
However, planted tank folks keeping discus do not have that goal, they also want the tank to look nice and more natural and tend not to be so concerned about feedlot style fish culture...........so there's some trade offs.
The biggest misconception is the issue about the source of the NO3, KNO3 vs fish food/waste.
Regards,
Tom Barr