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Good point about activity from Biospira and not much from rock. If the typical live rock is like your “lazy sand”, the hobby might be overestimating the capacity of live rock to oxidize ammonia though it would be a excellent source of bacteria as Aquabiomics has demonstrated.
It would be interesting to know the ammonia oxidation rate for your live rock before adding anything. There might be a simple way to roughly estimate the volume and surface area so we could compare its capacity to your sand.
I recollect an experiment done some time ago comparing the nitrification/denitrification capacity of live rock vs. live sand (just can't find it on the Internet). In this experiment, live sand was found to be much more effective than live rock.
The experiment I linked to a post or two above shows:
"The results demonstrated that LR mainly removed ammonium (NH4⁺) from the water with a mean efficiency of 0.141 mg/(kg·h), while the removal of nitrate (NO3–) was not significant. Bacterial diversity analysis showed that ammonia-oxidizing bacteria (AOB) were the most common bacteria on LR, which accounted for 0.5%–1.4% of the total bacterial population, followed by denitrifying bacteria, which accounted for 0.2% of the total population, and the ammonia-oxidizing archaea (AOA) were the least common type (<0.01%). The low abundance of denitrifying bacteria may be responsible for the poor nitrate (NO3–) removal of LR"
My take away from this is that while live rock is not very effective at direct nitrification/denitrification, it actually is beneficial since it does process ammonium , thus resulting in less nitrite/nitrate being produced.
One additional feature of live rock not often discussed is the surface community of periphyton/biofilms. These communities are very effective at capturing/sequestering POM (particulate organic matter), which helps to keep a system oligotrophic and the water clear. The surface biofilms also contribute to denitrification as indicated in the Reefs.com article.
"The results of this study stand in stark contrast to the prevailing wisdom, finding that “live rock” had no noticeable effect on nitrate levels during the 96-hour trial. And, somewhat counterintuitively, it was also shown that the denitrifying bacteria are up to 15 times more abundant on the surface of “live rock” than within it."