Deep Sand Beds

A deep sand bed (DSB) is a method of biological filtration commonly used in saltwater aquariums. Deep sand beds consist of  a substrate with a depth of 3-6 inches are more and are designed to cultivate anaerobic bacteria in the bottom layers of sand. These bacteria convert nitrate to nitrogen gas removing toxic substances from the water. Deep Sand Beds can act both as a nitrate filter and a supplementary calcium reactor.

Materials commonly used include coral rubble, crushed marble, pool dust, broken shells, etc. All of these are generally composed of aragonite or calcite, with aragonite favored for its greater solubility and capacity to buffer seawater. Typically superfine sand is used with a grain size of 1mm and 0.05mm. Finer grains readily dissolve and are capable of supporting a greater diversity of biotic activity. A larger size is slower to dissolve and could be too heavy for smaller delicate organisms to excavate. Larger sizes are also more likely to trap detritus. This could adversely affect water quality if not agitated by water flow or sand stirring by aquarist or tank inhabitants. A high quality fine grain sand will create a deep sand bed which may never need cleaning.

 Water flow through the sand bed is achieved by diffusion and the movement of organisms such as worms, crabs, snails, and stars. These invertebrates dig through the top inch or so of sand searching for food and help circulate water much deeper into the sand than would be possible without their aid. Healthy Deep Sand Beds are an attractive addition to any aquarium with many interesting organisms on display in a constantly evolving ecosystem.

Newly established Deep Sand Beds should be “seeded” with sand and/or live rock from a previously established aquarium. This will speed up the curing process of your tank and lead to a rapid expansion of life within the sand bed. Over time, sand will need to be replenished in order to replace dissolved sand.