Mastering Freshwater Aquarium Ecosystems
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Substrate plays an important part in the health of an aquarium ecosystem. Substrate is colonized by both aerobic and anaerobic bacteria, that aid in the nitrification of ammonia and nitrite, and the denitrification of nitrate. The substrate develops overtime separate and distinct environments within the bed.

Depending on the size of the substrate that is used, different populations of bacteria will develop at different depths in the bed. On the top layer of the substrate that is in contract with the oxygen rich water column, high densities of aerobic bacteria that are responsible for the nitrification of ammonia and nitrite will develop. In the lower depths of the substrate where very little water is exchanged, a anaerobic (no oxygen) environment develops, that is the primary habitat of anaerobic bacteria. Anaerobic bacteria use the oxygen in nitrate to respire. The anaerobic bacteria that breaks down the nitrate will eventually release nitrogen gas (non-toxic) that will bubble out of the aquarium.

Fine grain sand will develop an anaerobic layer at a shallow depth in as little as ¼ inch (6 mm) in depth. The larger the substrate size, the greater the depth needs to be before the aquarium ecosystem can benefit from denitrification. Larger substrates marketed for aquarium use may require several inches before an anaerobic layer will develop.


Fine #60 natural sand is used in this aquarium.

Substrate comes in many sizes and colors. The color of the substrate can affect how dark some fishes color will be displayed. Some species of fish will have a darker color over dark substrate. The size of the substrate should also be considered, depending on the type of fish, plants, filtration, and spawning behavior.

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