LR and filters

[Aquattro]

The breakdown of NH3/NH4 by (aerobic) bacteria happens independantly of light. This is also true of the next step from NO2 to NO3. Anaerobic bacteria then further metabolize the NO3 into N2, free nitrogen gas. Again, light is not a factor.
The original question of adding LR rubble to a canister is a good question. The difference will only depend on the surface area of the substrate, whether it be LR or ceramic rings. I don't know which is greater. They will both filter in the same manner as the other.