I'm no good for fish specifics/lateral pass to my large tank peers my tanks are only tiny coral displays no room for fish to study. You can pick up my reef tank full running and move it to a new table if desired ha = no fish in microtanks the thread police 'll get ya.
but it's really fun science to study bioloading vs surface area vs microbiology (keeps tiny coral displays running nicely, upscales and downscales to all size aquaria) and for sure if you stack marine pure blocks, or any alternate surface area in the sump, you can run any normal bioloading fish-wise the tank could reasonably run even if it had rock
These surfaces need to be cleaned, evacuated of pore-plugging waste regularly as this keeps vital surface area open vs ever-reducing
There are benefits to rockless setups, namely accessibility which is core in fish management, cleaning, tank maintenance
I like your approach as it's opposite of most reefs but can still keep same animals. You are re assigning oxidation to sand and marine pure surfaces, can be done on demand.