I deep sea bed (DSB) was all the rage 10 years ago. And is still in use with many reef type tanks.
But then about 5 years ago some reported all the sudden crashes.
So people started talking much more about refugiums with macro algaes. and also algae turf scrubbers (again).
the DSB works with anoxic bacteria to reduce nitrates to nitrItes then to nitrogen gas.
But if it is not work correctly some evil bacteria can actually further reduces the nitrItes to ammonia.
So you wind up with an aerobic cycle ammonia->nitrItes->nitrates.
and an anaerobic nitrates->nitrItes->ammonia. (plus possibly releaseing some sulfur in the process)
And to top all that off the surface of the substrate has low oxygen (high carbon dioxide) and nitrogen gas. The exact requirements for cyano bacteria. so after a few months of operation, nitrates drop down and then here comes a huge cyano bloom.
so some like me just use FW plants and marine macro algaes so the cycle is: