Fish tank filters and heaters are two of the most important components of a successful aquarium setup. Filters are what keeps the water from becoming stagnant and lifeless. Filters have three purposes. Filters are the breeding ground for the special bacteria that works with the chemicals produced by the fish waste. This is crucial for the biological cycles of your tank. Filters also remove the debris from the water, and finally, some filters allow you to place active carbon and other chemicals when they are needed in the tank.
In the category of internal filters, you will dab rigs under find the under gravel filters that are normally used in freshwater tanks. An under gravel filter is a raised grate on the bottom of the tank, under the gravel or any other substrate you want to use. This grate has two holes where you will attach a pair of vertical plastic tubes. These tubes work with either a power head or a bubbler inside them. The way it works, is that the water is forced to flow through the gravel to go under the grate, where it will go up the tube and into the tank. The gravel itself works as the filter media. It collects the leftover food and waste.
Another kind of internal filter is a sump tank placed below the main tank. This kind of filter is used for salt water tanks. It works like this: the water from the fish tank spills into an overflow, which has a pipe leading to the sump. The sump contains filter media and a pump, which sucks the water in and then pushes it through a tube back into the main tank. The disadvantage of this kind of filter is that it can be expensive and it can also be noisy.
The preferred kind of filter is the external kind. There is the kind that you can hang from the back of the tank, and the kind that goes underneath, in the stand. All the filtering happens there. The water gets sucked out into the filter, passes through the filter media and goes back into the tank. This type of filter can be expensive, but it is also the most effective and low maintenance. You just need to make sure that the filter is large enough for your tank size. It has to be able to circulate ten times the volume of water per hour. A 75 gallon fish tank needs a filter that can circulate 750 gallons per hour.