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Filtration In Aquarium. |
Filtration
Water in the aquarium is stagnant and there is potential for build up of organic toxins from uneaten food, decaying plants, dead fishes, waste products from fishes, etc. A remedy to this problem is continual partial water changes. A better option which can obviate the need for tedious water changes and give greater protection and clarity is to install a filter.
Filters are available in many shapes, sizes and prices. In a filter the water is passed through a container in which suspended impurities are trapped by the filter medium and the clean water is then returned to the aquarium. Modern filters in addition to maintaining water clarity can also be used to alter the water’s pH or hardness to some degree. There are three basic types of filters used commonly in aquaria – mechanical, chemical, and biological. They are fitted either inside or outside the tank. Most mechanical or chemical filters are box or cylindrical shaped containers holding the necessary filter media through which the water is passed.
The sub-gravel biological filter
Biological filtration is the use of bacterial action to clean the water and utilizes the gravel of the aquarium as the filter medium, not as a trapping device but as a home for colonies of aerobic bacteria. Water is circulated through the gravel either downwards, or upwards in the reverse-flow systems, by a system of plates or tubes beneath the gravel, (This filter is put into the empty tank before anything else when setting up.) Bacteria living on the surface of each grain of gravel break down the toxic substances into non-toxic compounds; this system is essential in marine aquaria, where the biological action keeps the dangerous nitrogenous level down to a safe minimum. To work efficiently, the sub-gravel filter should cover the whole area of the tank base. It is not recommended for use in aquaria where fishes that dig into the gravel are to be kept; their uncovering of the filter plates or tubes will only short-circuit the operation of the filter, as the water will prefer to go directly through the exposed part of the filter rather than through the gravel. It is also essential that the air supply to this type of filter is never turned off; as soon as the water flow ceases, the aerobic bacteria will begin to die for want of oxygen, and pollution of the tank will begin.
A criticism of this type of filtration when used in freshwater aquaria is the adverse effect on plant growth experienced by some aquarists. To minimize this, the depth of the gravel should be at least 5-8 c.m (2-3 inches) above the filter plates. Many aquarists grow their specimen plants in shallow pots buried in the gravel, where they will not be disturbed by any filter action.
One positive advantage of this form of filtration if that no maintenance is necessary (or possible); as long as air is supplied to the system, it works.
Constructing an under gravel biological filter system
The hobbyist can make his own filter system at, perhaps, a fraction of the cost of a commercially produced unit. The materials used are corrugated plastic sheet and plastic pipe and fittings used by the plumbing trade. A few saw crusts across the ‘ridges’ of the corrugated sheet soon produce the slots through which the water passes, and the plastic pit is glued into a hole at one end of the sheet to form an airlift. In this way, under gravel filters can be tailor-made to fit aquariums of any dimensions. A word of warning: non-toxic materials must be used. Some aquarists periodically attach a tube to the airlift and siphon out any collected silt from beneath the filter bed. When first fitted to the aquarium, the filter bed takes a time to mature-that is, for the bacterial colony to become established. This process can be fastened by the addition of some water or gravel from an already established aquarium, or the filter bed can be ‘seeded’ with a small piece of meat, which is allowed to rot away.
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