Midwater
I'd be curious, to see some simple testing (if you have the time, and energy) in or around the waters near where you live?
To see, if the same is true there where Dats live, as in tropical areas that match up with tropical areas in Panama where my cichlids come from.
So often we see erroneous info that our fish come from nutrient nitrate filled areas.
yet where I test, nitrates are non-exiistant.
It seems to me aquarists are often bamboozled into a false sense of nitrate reality, when the truth is far and away totally different.
On a side note
one other alternative to the use of a full sump, is the use terrestrial or aquatic plants in the main tank itself, to somewhat reduce the excessive nitrate load.
I use house plants with roots in the tank, along side the aquatic plants wherever possible.