Thanks for your detailed answer Peter.
I agree with you, that an aquarium with blackwater fish is not comparable with high tech aquariums, because we dont use strong light, CO2 and hard neutral water. “Our systems are running slower”. I agree with you too, that its better not to use fertilizers with nitrate and phosphate.
But in some points I do not agree with you. Let me explain.
We can not copy natural systems in the aquarium. We have always (in relation) a very high input of food in the aquarium. So we have eutrophic water. We must take the nutrients away. We can do that with waterchange and harvesting of biomass. So our aquarium IS comparable with agriculture or farming.
On the other hand we use RO-water or rainwater without minerals. 2-5 % of the minerals remain in RO-water. The content of macronutrients (Mg, Ca…) is enough (because plants do not need a lot of them). But micronutrients are even in very low concentrations in tap water, in RO-water the content is near zero. To enhence the plant growth we have to add Fe, Mn, Zn…!
Harvesting plants can help us to reduce water changes. The better the plants grow, less water must be changed. And water changes always change water values (humic and fulvic acids, DOC, pH, hardiness). In my opinion the more stable system is the system that do not need big water changes.