Cooling: lighting, pumps, filters and other electrical items within the aquarium all add to the overall temperature, often exceeding the requirements of even tropical animals in the aquarium. This is especially true of today's modern marine aquariums where temperature is critical to many corals and fish. In order to guarantee a stable temperature in any aquarium a refrigeration unit ( made from non corrosive titanium ) called a 'chiller' is usually 'hooked up' via a pump from the aquarium or sump. This will guarantee a stable temperature range. It is always advisable to choose a 'chiller' larger than required, due to ambient temperatures and lighting.