Fish that Eat Feces
Within the restricted environment of the aquarium there take place several complex processes which need to work efficiently if the tank is to remain healthy. Both fish and plants have some specific requirements, and the tank must be set up in accordance with these.
The fishes’ waste products, uneaten food and dead plant material are all broken down by bacteria. The fishes’ urine contains ammonia substance, but the bacteria warming in the tank quickly convert this to less toxic nitrites.
These are in turn broken down again by bacteria to relatively harmless nitrates, which are used by and encourage the growth of fishes.
Fish feces, uneaten food, decaying plant material and living and dead micro-organisms form a thick sediment called mum, which settles to the bottom of the tank and accumulates in corners and behind plants. More bacteria breed in this mum, which is constantly stirred up as Catfish, Loaches and other fish grub about in search for food. Not only is mum unsightly, it can also be a source of health problems if it builds up to high levels, when bacterial decay may deplete oxygen.
The mum can be removed, and the water kept sparklingly clear, by using simple filters powered by the air supply from the aerator pump. Air-powered filters all depend on a simple principle: as air bubbles rise to the surface, they carry a flow of water with them. If the bubbles are confined in a vertical tube, they can lift the water above the tank surface. This simple device is called bauble airlift. In its simplest form, the bubble lift can be used tore move coarse mum and surplus dried food from the tank, by drawing the water through a filter medium.
Cheapest and simplest is the corner filter, a small plastic box which sits on the surface of the aquarium gravel and has a bubble airlift protruding from its upper surface. The lower part of the boxes perforated, and it is packed with fine ethylene fibers which act as a filter medium. (Never use glass fiber for this purpose. It can be serious health hazard.) As the bubble airlift operates, it draws water in through the perforations in the box and so traps suspended waste materials in the filter medium. The corner filter operates continuously, and needs cleaning only every few weeks, when it is removed and the filter medium replaced. As with other filters using the bubble airlift, this one has the advantage of help in aeration and maintaining good water circulation. It is, how-ever, large and unsightly, and if possible should be hidden behind plants or rocks.
This problem is overcome by using an outside filter, which hangs over the side or rear of the tank. The airlift draws water and sediment from the bottom of the tank through an inconspicuous plastic tube, lifting it out of the tank and into a plastic box con-tainting filter medium. Cleaned water then returns to the tank through a short siphon tube. This type of filter has some important advantages, chief of which is that it can be cleaned out with minimum of disturbance of tank or fish. In addition, the filter chamber can be quite large, and so needs less frequent cleaning.
It may be desirable to put other materials into the filter chamber. Peat may be added when breeding certain acid-loving fish. Charcoal is sometimes used to remove damaging substances from very ‘old’ water. But these are exceptional circumstances: for normal use, filters of this type operate for years with a minimum of fuss or maintenance.
Probably the most important type of filter is the ‘biological’ filter, or sub gravel type. This consists of a large plastic plate, saner the size of the tank bottom as possible, which contains many perforations or slits to allow water to pass through. It incorporates small ‘feet’ which hold it about LCM (1/tin) above the tank bottom. Some older designs consist of a grid of interlinked perforated tubes.
At the rear corner of the filter plate is a bubble airlift. The \whole plate is covered with a layer of gravel at least 7.5cm (3in) thick. As the airlift operates, water is drawn down into the grave land through the slits in the filter plate, before ascending the airlift and being discharged. Mu1m is drawn into the gravel, which thus acts as the filter medium. This system is attractive in its simplicity, and has some important advantages — as well as some disadvantages.
Mum trapped in the gravel is broken down by bacteria handmade harmless. Normally, in deep gravel, bacterial action occurs under conditions that are anaerobic; that is, lacking in oxygen.