provides a place for anaerobic bacteria to flourish is quantity, and provide a denitrifying effect (removal of nitrate and the production of non-organic nitrogen gas). The inherent risk with a DSB
is the potential for a build up of H2S gas, a toxic nerve gas that, if allowed to build up and then be disturbed, can wipe out a tank.
If you have a macro algae in your sump, then you already have a nitrate consuming method, and a DSB
is not required. A bare bottom sump is much easier to maintain too.