I have had my 75 Gal Discus running for nearly 3 yrs. It is well planted(heavily) and somewhat overstocked(6 adults=5"; 1 runt;2 big angels and 3 clowns)
I have used 3/4 tsp kno4,<1/4 KH2PO4 mixed in 1/2 gal h20.
I add macros @ change and 20 ml csm+b evry other day. Simple EI
I do a 60% water change every 5-8days straight out of tap using Prime.
Havent lost a fish;little algae(spot)
Discus are more tolerant than we are led to believe.
Stable conditions and clean water(plants)
I have also made a habit of doing gravel vacumn at change.
75 Gal Discus,Crypts,Bacopa,Vals,Ludwigia,Java Fern,Hygro+2 Swords,Alternanthera,java moss ,anubias,P.stellata,lotus
12 Gal Nano, Shrimp,Pygmy Corys,Riccia, Ludwigia,, crypts, HC,nana petite