Reef Aquariums | Biological Filtration in the Reef Aquarium

Biological Filtration in the Reef Aquarium


Filed Under filtration, reef aquariums |

Previously we talked about mechanical and chemical filtration. Today we will discuss biological filtration in the reef aquarium. There are three schools of thought on the subject: the predominantly used Berlin and Turf Scrubber methods, and the recently more popularized Jaubert System.

In a closed aquatic system, such as any home aquarium, any nutrients readily available either live or grow there. The owners periodically feed the inhabitants some manner of fresh, frozen, or freeze-dried cuisine to the inhabitants in an effort to sustain them. Any excess food falls typically past the swimmers in the water column, into the depths where it is consumed by the scavengers and other similar inhabitants. Anything not eaten falls into various nooks and crannies in the rocks and substrate of the aquarium. Much like food left open in the air for an extended time, excesses food in a marine environment begins to decompose.

In any system, both decomposing food and waste produced by the tank inhabitants are converted by bacterium into a toxic chemical known as NH4 or, more commonly, ammonia. In even small amounts, this ammonia readily kills the inhabitants of most aquaria. Nitrosomonas bacterium, a species of bacteria that eats ammonia, devour the ammonia and produce NO2, or nitrite, as their waste product. While organic, nitrite is still toxic to aquarium inhabitants. Nitrobacter bacterium, a species of bacteria that eats nitrite, consume the NO2 and produce NO3, nitrate, as waste. Nitrate is more readily known as a common plant fertilizer.Nitrate is not a toxin in the same manner as ammonia and nitrite.

Most inhabitants are able to handle a reasonable amount of nitrate, fish better than invertebrates. At high levels nitrate begins to alter the environment and render it inhospitable by causing chemical changes to the water. At very high levels, the nitrate renders the water toxic. In general, nitrate levels are something an aquarist can tend to using any or all of the methods from the three schools of thought of reef keeping. It is important to note that none of the three methods is fixed in stone and their use and adaptation are reasonably flexible.

Reef aquaria today typically contain several inches of sand on which sit many pounds of rocks that came from the sea. The rocks are large and numerous and consume close to 50% of the volume of the aquarium. These porous rocks arrive from parts of the world such as Fiji, St Martial Islands, and Papa New Guinea, and are covered with various algae, plants, and marine life. Each of these organisms plays a role in the mariner environment; however, it is the smaller organisms, those invisible to the naked eye that are within the rocks that make all the difference.

The porous nature of the rock allows for surface areas greater than that of the exterior of the rock. The large surface area provides homes for the Nitrobacter bacterium. These bacteria consume the nitrate and produce nitrogen (N2) as waste. The removal of nitrate, or denitrification, by the bacteria in the rock makes it an essential component in completing the nitrogen cycle. Because the bacteria live well within the rocks, the water in the aquarium must be circulated with sufficient force that some part of it reaches the center of the rocks.This mix of a sand and live rock with water movement circulation throughout the tank is known as the berlin method.

The Jaubert method substitutes the live rock for an sand bed which often ranges in 6-8" and is established over a plenum of some kind, usually an old undergravel filter. The goal is to have the bacteria colonize the deep sand bed and provide the same denitrification as the live rock. In both the Jaubert and Berlin methods, protein skimmers are an essential part of the filtration system.

The thirds camp of biological filtration is the algal turf scrubber. To accomplish this, water is routed from the aquarium into shallow trays in which turf algae are cultured. The algae growing in the trays use the nitrate in the water as their food source. The algae are then harvested as needed providing the export path of the waste.

For Tank 1.0, we decided to employ the Berlin method and have a 2-3" sand bed with 65 lbs of live rock in our aquarium. We hope that you will continue to follow along and learn about our reef aquarium.

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