Filters work in three ways: mechanical, chemical and biological. Basically speaking, a mechanical filter removes large particles suspended in the water, a chemical filter changes the chemical balance of the water, and a biological filter harnesses the cleansing power of colonies of bacteria to purify the water that flows through it. In practical terms, a simple biological filter performs all three types of filtration at the same time.
By far the best all-round biological filter is an under gravel filter. This usually consists of a corrugated piece of plastic with small holes or slots in it. In one corner there is a large round hole in which plastic uplift tube fits. The whole thing is placed on the bottom of the tank and covered with a layer of gravel substrate to a depth of about 5-7.5cm (2-3in). When the tank is filled with water and an airline is placed down the uplift tube and connected to an air pump, the air bubbles rising to the surface in the tube draw water up with them and set up a flow of water down through the gravel layer over the entire base of the tank. In effect, the gravel acts like tank-wide filter bed. Not only does this strain out suspended particles, but after a few hours, colonies of useful aerobic bacteria start to develop in the oxygen-rich conditions in the gravel, and over a period of weeks these will multiply and do battle with any harmful bacteria and chemical waste products. Instead of using rising air to power this type of filter system, a water pump can be fitted on the top of the uplift tube. This so-called 'power head' increases the flow rate through the filter bed and up to point improves the efficiency of its filtration action.
Various alternative biological filter media are available; these are usually little ceramic rings or complicated plastic shapes with a large surface area for bacteria to grow on. External power filters are very versatile and when filled with a suitable medium, such as sponge or aquarium floss, they can also be used as mechanical filters. In fact, good combination is to use an external power filter to mechanically clean up the water that flows through an under gravel filter in the tank.
Other types of mechanical filter include simple power filters that fit inside the tank and air-powered box filters filled with aquarium floss that also go inside the aquarium. There are also sponge filters; these have their own air uplift and draw water through a cylinder of sponge. These give good mechanical filtration with quite a bit of biological action as bacteria grow within the sponge.
The air supply for filters comes from an air pump. These are obtainable from aquarium shops in a range of types and prices. Some make more noise than others and this may be an important consideration for a tank set up in the living room. Do not be tempted to use air pumps intended for anything other than aquariums; these pumps can have oils in them and if fish come in contact with oils of any type, they will die. Your aquarium dealer will be able to supply you with clear plastic tubing - universally called airline - which attaches to the pump and runs to the aquarium. The dealer will also supply valves, T-pieces and clamps so that you can run several airlines from one pump and adjust their flow to various pieces of equipment as required. Make sure that your pump is placed above the water level so that if for any reason the pump should stop, water will not siphon back through it and onto the floor. If you cannot place the pump above the water level then fit a non-return valve in the airline near your pump. This will allow air to pass towards the tank but stops water flowing back.
An air supply is also needed in the tank in order to help the fish breathe. This is usually accomplished by passing air from the pump through an air stone that splits the air into masses of tiny bubbles. The rising column of bubbles moves the water around and, in doings, helps it to absorb oxygen from the surface. There are many types and sizes of air stones; some are pieces of wood, others consist of sand particles glued together. Some dramatic effects can be created by positioning firestones so that they bubble up from tinder rocks or from underneath the layer of gravel on the base of the aquarium.
Various alternative biological filter media are available; these are usually little ceramic rings or complicated plastic shapes with a large surface area for bacteria to grow on. External power filters are very versatile and when filled with a suitable medium, such as sponge or aquarium floss, they can also be used as mechanical filters. In fact, good combination is to use an external power filter to mechanically clean up the water that flows through an under gravel filter in the tank.
Other types of mechanical filter include simple power filters that fit inside the tank and air-powered box filters filled with aquarium floss that also go inside the aquarium. There are also sponge filters; these have their own air uplift and draw water through a cylinder of sponge. These give good mechanical filtration with quite a bit of biological action as bacteria grow within the sponge.
The air supply for filters comes from an air pump. These are obtainable from aquarium shops in a range of types and prices. Some make more noise than others and this may be an important consideration for a tank set up in the living room. Do not be tempted to use air pumps intended for anything other than aquariums; these pumps can have oils in them and if fish come in contact with oils of any type, they will die. Your aquarium dealer will be able to supply you with clear plastic tubing - universally called airline - which attaches to the pump and runs to the aquarium. The dealer will also supply valves, T-pieces and clamps so that you can run several airlines from one pump and adjust their flow to various pieces of equipment as required. Make sure that your pump is placed above the water level so that if for any reason the pump should stop, water will not siphon back through it and onto the floor. If you cannot place the pump above the water level then fit a non-return valve in the airline near your pump. This will allow air to pass towards the tank but stops water flowing back.
An air supply is also needed in the tank in order to help the fish breathe. This is usually accomplished by passing air from the pump through an air stone that splits the air into masses of tiny bubbles. The rising column of bubbles moves the water around and in so doing helps it to absorb oxygen from the surface.