DSB (Deep Sand Bed)
Deep sand bed (10-15 cm) creating anaerobic zones for denitrification. A natural method to remove nitrates.
Detailed explanation
The Deep Sand Bed is a natural filtration technique that uses a very deep bed of fine sand to create an oxygen gradient. The superficial layers are aerobic and host nitrifying bacteria. As you go deeper, oxygen decreases until it creates completely anaerobic zones where denitrification occurs.
The sand must be fine (0.5-1mm grain size, preferably aragonite) and the layer must be at least 10 cm. Below 10 cm the gradient does not develop correctly. Many supporters of the method recommend 12-15 cm.
DSB works best with abundant microfauna. Worms, small crustaceans, serpentine stars and snails that burrow into the substrate keep the sand moving, preventing pockets of toxic gas from forming.
The debate on DSB is heated in the aquarium community. Proponents say a well-managed DSB keeps nitrates at zero without needing frequent water changes. Detractors warn that after 3-5 years the DSB can "crash", suddenly releasing hydrogen sulfide and accumulated toxic substances.
Remote DSB in the sump is a popular compromise. You hold a deep DSB in a separate sump chamber, away from the display. If something goes wrong it can be removed without upsetting the main aquarium.
The modern alternative to DSB in display is bare bottom with a biopellet reactor or other denitrification systems.
In freshwater aquariums the concept of DSB exists but is less widespread. A deep nutrient substrate for plants performs a similar function in a less risky way.