There are three major types of filtration used in marine aquariums -- mechanical, chemical and biological. A good mixture utilizing all three types of filtration would be advisable Biological filtration utilizes bacteria to break down waste material in the water. During mechanical filtration, small particles in the water pass through the filter media and get caught. Example of this would be rapid sand filters in large aquariums and simple foam pads in home aquariums. Chemical filters may utilize activated carbon to remove dissolved molecules from the water. Another example of a chemical filter would be a protein foam skimmer. All types of filtration are readily available in most aquarium shops.

Undergravel filtration is a simple way to filter the aquarium. It is usually made of a flat plate or screen which is set up off the aquarium bottom, leaving a small empty space below it. Filter media (usually gravel) is placed on top of the filter. there are at least two uplift tubes which are connected to the space below the filter and draw water up through them as a result of an air pump on the top of the tube. In this situation, the water passes down through the gravel and then back up to the surface of the aquarium through the uplift tubes.

An aquarium of 76 liters (20 gallons) or more is recommended for marine systems. For a freshwater system, it is recommended to begin with a 38 liter (10 gallon) aquarium.

They types of filtration elements described in the previous section can be used in both freshwater and marine aquariums. An undergravel filter with at least one or two airlift tubes is advisable for most systems.

Most types of gravel will work for a freshwater system. A gravel is calcareous (containing calcium) is recommended for marine systems, although it is not recommended for fresh water systems that require a low pH. The gravel should be 2-3 inches thick on top of the undergravel filter to provide the correct filtering capacity of the aquarium.

A filter unit which consists of a plastic compartment that hangs on the outside of the aquarium is another good filter to use. It pulls water from the aquarium and runs it through both a filter fiber and activated carbon. This also does a good job of circulating the water.

There are many different styles and sizes of air pumps that can be used for aquariums. The size of the air pump depends upon the size of the aquarium in use. Standard air-line tubing can be found in all aquarium shops. An air stone should be placed at the end of the tubing and placed in the airlift tubes. This will provide air and circulation to your aquarium and will also help the undergravel filter to operate normally. Powerhead pumps also help to circulate water and some are equipped with a venturi that helps to aerate.

The temperature of the water is very important. If there are variances in the temperature of the water it can lead to the demise of all the animal life. A constant temperature is recommended. Tropical aquariums do well at temperatures of 23 to 28 C (73 to 82 F). There are many different types of heaters available. The correct size is determined by the number of liters of water in the aquarium. Normally the heater should be two watts to every liter in the aquarium.

The aquarium should be covered at all times. The covers reduce evaporation and also keep the fish from jumping out of the aquarium. Most reflectors or hoods are made of plastic or stainless steel. If you have a saltwater aquarium, the hood should be a noncorrosive material. It is advisable to choose a hood with a florescent lamp.

The new aquarium should be filled with water to check for leaks before setting up your filtration. The undergravel filter should be placed in the empty aquarium first (the water is the last part added to the aquarium). The new gravel should be rinsed before being set into place because it normally is very dusty. Assemble the air line tubing and outside filter according to the directions. The activated carbon should be rinsed before use because it is also dusty. Finally, add the water to the aquarium. The air pumps, the outside filter and the heater can be turned on once the aquarium is full of water.

Once the aquarium is in place, it should run for at least 24 hours before adding any animals. The levels of pH, salinity, temperature and ammonia should be checked to be sure they are all at acceptable levels. The addition of live plants or one small inexpensive fish may help to initiate the biological filtration. Once all levels are acceptable for your particular style of aquarium, fish can be added to the aquarium.