Bio media is all about space for bacteria to live on, and amount of water flow over it.
I have sumps filled with lava rock that works fabulous.

Moving/fluidized beds are about the bacterial living space, and flow, and the theory that as the old bacteria become less effective, they are sloughed off, and replaced by more viable bacteria.
I use 4 ft fluidized columns of aragonite sand, so beside bacteria colonizing the sand, the sand also acts as a pH buffer. The sand is dissolved by acids (fish urine) thus neutralizing it.


I have seen the fluidized columns over 8ft high in densely stocked aquaculture systems.
I have sumps filled with lava rock that works fabulous.

Moving/fluidized beds are about the bacterial living space, and flow, and the theory that as the old bacteria become less effective, they are sloughed off, and replaced by more viable bacteria.
I use 4 ft fluidized columns of aragonite sand, so beside bacteria colonizing the sand, the sand also acts as a pH buffer. The sand is dissolved by acids (fish urine) thus neutralizing it.


I have seen the fluidized columns over 8ft high in densely stocked aquaculture systems.