A constant, appropriate water temperature is vital to keeping your aquarium's inhabitants healthy. A sudden temperature change can place undue stress on your aquatic life, increasing their susceptibility to infection and disease.

Aquarium setups - reef aquariums in particular - often employ equipment, lighting and water pumps especially, that produces enough heat to raise water temperature. Without a chiller to decrease water temperature, aquarium water can warm to a point where it no longer holds enough oxygen to sustain the inhabitants.

Chillers are by far the best method of cooling an aquarium. Chillers are basically heat exchangers. Most chillers use titanium coils and a refrigerant to cool the water as it passes by the coils.

There are three types of chillers available on the market today, inline, drop-in, and thermoelectric.

The inline chillers require water to be pumped through the unit. The cooling of the water will occur within the coils located inside the chiller. These chillers can be placed anywhere in relation to the tank. For example the chiller can be placed outdoors (in a protected shelter), in a garage or in a different room as long as the user is able to pump water into the unit.

The drop-in chillers have the titanium coils external to the actual unit. The coils need to be placed into the sump where water can pass by the coils to be cooled. The advantage to this type of a chiller is there is no plumbing needed, so it is very simple to install. One of the disadvantages of the unit is it needs to be placed right next to the sump as the coils and flexible refrigeration line coming from the chiller are normally around 3-5 feet long.

Thermoelectric chillers are quiet and energy-efficient. Thermoelectric chillers, such as the Cool Works IceProbe, are intended for use with smaller freshwater and saltwater aquariums, less than 55 gallons, and insulated bait/specimen tanks with a slow water flow. Thermoelectric chillers are not effective on large aquariums with a fast water flow.