Live rock is fine, but the goal of it is to have surfaces resistant to algae, not to add bacteria.
Why not add bacteria? The big advantage of live rock is that it introduces complete, working microbiomes. To reduce bacteria to nitrifying bacteria is not a good approach in my eyes, not for good and not for bad. I doubt that live rock introduces much nitrifying bacteria, maybe nitrifying archaea (may seem like hairsplitting). For nitrifying bacteria the ammonium concentrations in NSW are too low. It is mainly archaea that do the nitrification in NSW and oligotrophic tanks.
Calcareous surfaces may have a dual function: Being substrate for bacteria and buffering phosphate. In fact the large surface of a coral sand substrate may act more as a source and buffer for phosphate than as substrate for nitrifyers, especially when starting a reef tank. Phosphate concentration and phosphate supply of coral sand usually is quite high.
One observation I’ve noticed is that most (not all) nuisance algae require at least a hard edge or porous material to cling to. Smooth surfaces such as acrylics and plastics don’t seem to be great real estate. Coralline however loves these smooth surfaces. I can put a picece of plastic in my tank and see coralline within 2 weeks.
I say this because I’ve pondered doing a very similar set up, except with no rock and only plastics, adding corals first and a source of nitrogen and phosphorus.
Plastics are lipophilic in contrast to many other surfaces. Lipophilic surfaces attract bacteria. Most macroalgae including coralline algae need some bacterial "companions" that produce vitamins and/or other growth promoting substances the algal parners need. The algal partners give organic carbon compounds (slimy surface) to the bacteria in exchange.
Is it true that there is nothing we can do about that? I think the experiment would be even more compelling with an antibiotic, though I’m not sure how livestock would fare in a sterile environment, aside from the impact to nitrogen cycle.
Archaea are not sensitive to the usal antibiotics. I think in many tanks antibiotics have been used unknowingly to eradicate cyanobacteria and not always with severe detrimental effects or maybe sometimes without detrimental effects at all. Archaea are a much underestimated and often unknown part of the microbial communities, especially inside organisms like sponges or corals.
Having equal or more ammonia uptake will lead to zero NO3. The only way around that is to dose something daily, just enough to balance the few ppm of NO3 needed. Possible in a forever changing environment?
Who says a few ppm of NO3 are needed? I think this should be proven, maybe by RHF's experiment.
As far as possible ideas for the article. For me it would be interesting to see the time frames in which corals can consume NH3 compared to nitrifiers if that is even testable.
This is already known. The "time frames" (and more important the concentrations) at which in biochemistry uptake of something occurs is described by uptake kinetics which is typically a
Michaelis-Menten kinetics. You can find
uptake kinetics of Stylophora here.
Nitrifying bacteria need much higher ammonia/ammonium concentrations than corals to show any uptake. Here mainly archaea are relevant. I know there are articles around comparing uptake of ammonium by ammonia oxidizing bacteria AOB with that of ammonia oxidizing archaea AOA, but I am not sure that such comparisons are of too much help. Conditions in reef tanks are complex with spatial and temporal patchiness of nutrients. For example AOA may sit at places where ammonia is produced, for example inside sponges or at other filter feeders. Corals may benefit from fish and coral crabs hiding between branches.
