Many folks considering the jump to saltwater aquarium keeping are confused by all the options and variations available in filtration. We would like to give you a brief overview of each of the more popular methods out there and how they relate to your project.
Without going into theory, the primary function of all filtration in marine aquaria revolves around providing ample area for necessary beneficial bacteria colonies. The establishment of these colonies by process of the biological cycle is crucial to any successful aquarium setup, be it fish-only or a reef system. Our format will graph the method, the necessary equipment, and purpose of various types of filtration methods.
CHAPTER 1: Undergravel Filterplate (UGF)
Probably the most popular and most difficult system to maintain for any length of time. This method employs a plastic grid or plate under several inches of crushed coral sand or dolomite. The function of a UGF is to draw oxygenated water down through the gravel where the bacteria colonies reside. As only the top inch or so actually contain the bacteria's, cleaning and other maintenance issues are a delicate operation. Lift tubes with airstones are placed at the rear corners of the plate to facilitate a siphon that is created by a rising column of bubbles. Flow rates with these filters are determined by the number of tubes and the volume of air that is pumped into them. Most hobbyists use a pressure rated air pump like the Tetra Luft Pump or the Second Nature Whisper 1000. As the bubbles within the lift tubes rise, water is drawn from under the filter plate by negative water pressure. The unfiltered water is pulled down through the gravel, giving the aerobic bacteria bed everything it needs to convert ammonia's to nitrites and then into nitrate. For smaller systems having a light bioload, this is amongst the most affordable means of converting wastes.
This is the primary training filtration system used by neophyte aquarists. Low tech, affordable and easy to set up. However, this method of filtration is very limited in what it can provide for the advancing hobbyist. A very tight control on fish loading is necessary with UGF's, (undergravel filters). Because of the limited amount of surface area available for colony expansion, adding new fish can be problematic, once the loading limits of 1" of fish per 5 gallons of water is reached.
Another limitation of UGF's is the absence of available oxygen in the water. O-2 (oxygen) is held in solution up to about 7 or 8 ppm (parts per million) as DO (dissolved oxygen). Continuous O-2 stripping occurs as the water passes through the bacteria-laden gravel bed. The bubbles in the lift tubes help to replenish some of this depleted air, but cannot hope to keep up with the demand placed upon it by a dead or decaying animal within the system. This is a contributing factor when looking at fish and invert mortality rates when using these filters. Supplemental filtration is often recommended to augment the available bacteria beds and other mechanical filtration chores. This usually takes the form of a hang-on box filter or canister, looped to the display tank.
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