Vale, you have written a very informative posting stressing the fact that we really don’t know much about the processes within blackwater aquaria.
Nearly all we know about the bacteria life in our tanks refers to the normal aquarium with much higher pH and conductivity. And there is much of “wrong knowledge” as the stability of water values in aquaria is concerned, f.i. that a tank with no calcium will not remain stable as pH is concerned. This is simply false since the humine substances in a blackwater aquarium will act in similar a way than the missing calcium does in a normal tank. I mention this only as an example of the lack of knowledge in normal aquarium literature, that is entirely written to match the needs of normal aquarists with their normal fish from normal waters.
As you rightly point out the question of the role of bacteria is similarly bad understood as tanks with soft water and low pH are concerned; under these circumstances nitrification underlies different criteria than normally.
So, your information on the work of Tim Hovanec is very valuable indeed, and still more is that hint on those Canadian findings about the differences between Ammonia Oxidising Archaea compared to Ammonia Oxidising Bacteria. So there is a central statement of yours to be found in the words: “The more acidic the environment and/or the lower the concentration of nutrient (i.e. ammonia) the less likely it seems that bacteria will be the main oxidisers.”
I shall not go further into the interesting details you report of your own experiments; there is – of course – a difference between our European industrial products and those of the U.S., but I don’t think that “we” are much more efficient in controlling the nitrification of blackwater aquaria than you in the states. It’s only a fact that we establish such tanks quite successfully with rather a satisfying stability. But how things work and why things work and which components are responsible for it: this we all don’t know in sufficient detail.
Blackwater aquaria are possible and could be stable and beautiful, but they are only poorly understood at present. Your posting is one of the few contributions to the effort of pushing the frontiers a bit wider; thanks.