Tank

• All aquariums require some kind of tank, usually made of glass, with the edges of the glass panes sealed together with acrylic. Tanks come in all different shapes and sizes. They can be small, like a 10-gallon tank, or larger, like a 250-gallon tank. A tank may be rectangular, round, L-shaped, or any other of a varied of shapes.
  
  

Filter

• A combination of biological and mechanical filtration is often used. Filter systems are usually the most complex part of an aquarium. Biological filtration is used to control the nitrogen cycle in an aquarium, which is very important. Decomposing materials in an aquarium produce ammonia which can kill the fish. Mechanical filtration removes debris from the water. This debris may be food, waste or plant debris. The work done by mechanical filtration is rendered useless if the filter is not cleaned out, thus leaving debris to decay anyway. Besides for biological and mechanical filtration systems, there is also chemical filtration, which is used to remove dissolved debris from aquarium water.
  
  

Heater/Chiller

• An aquarium heater utilizes a heating element attached to a thermostat to control the temperature of the aquarium water. Where aquarium heaters are used to keep the water in an aquarium warmer than the surrounding air, chillers are used to keep the water cooler than the surrounding air for cold water aquariums. Thermometers are also used to monitor an aquarium's temperature. These thermometers may be glass alcohol, plastic or LCD.
  
  

Lighting

• Aquarium lighting is used to illuminate the aquarium in most cases. However, it may also be used to support certain life forms inside the aquarium. Lighting for a freshwater aquarium may be incandescent or fluorescent. Fluorescent may be preferred over incandescent lighting because it is brighter. Freshwater aquariums with plants may require a stronger light source than aquariums that only contain fish to encourage plant growth. Reef aquariums have a wide variety of lighting options. Some reefs require light in a certain spectrum, rather than traditional white light. High-output fluorescent bulbs are often favored for reef aquariums because of the brighter light they provide. Metal halide lighting is used when the shimmering effect that can be witnessed on the ocean is desired. There are even lighting units that simulate daytime and nighttime hours.
  
  

Decor

• Decor can be used in aquariums to create an environment that resembles a natural habitat as closely as possible, or simply to create an aquarium that is appealing to the human eye. Tiny pebbles of several different colors can be used to cover the bottom of the aquarium. They can also be used to anchor larger items of decor that would otherwise float to the top of the tank. Fake or real plants, as well as fake or real reefs can be used, with fake plants being made of plastic and anchored to the bottom of the tank with the pebbles. There are also aquarium decor items that are not meant, in any way, to resemble a kind of natural habitat, such as bubbling treasure chests and little ceramic divers.