Fish and invertebrates are cold blooded and hence you must be aware that their body temperature is controlled by the temperature of the habitat they live in. Water temperature in fish tank or Aquarium hence is a very important factor. Sudden fall or rise of even 5 degree temperature will become fatal for the fish. Hence its recommended to keep the water temperature stable. The fish requires optimal temperature range and not extreme. In India, certain regions are prone to extreme climate. The variance between day time temperature and night temperature varies from 5 degrees to 25 degrees. These can cause same change in water in a pond or fish tank. In such conditions we recommend use of heaters and chillers / aquarium fans. Continues cycles of temperature variance in water can cause stress to the fish and stress can cause various disease because during high stress the immune system doesn't work properly.More over increase in water temperature also decreases the Oxygen levels in water which again causes trouble. Apart from that algae can grow much faster in warm water and thus create a bigger issue for the pond or fish tank. How to choose a chiller The size of the chiller or fan is decided on various factors: How warm does the water gets? How much fund do you have to spend on intial and running cost? There are many brands of fans and chillers in the market. If you have a small tank, of the size of 50 - 300 Liters, we wont recommend a chiller. Reasons being the cost is not justified. You can buy fans which can mounted on the top of the fish tank and can be used. These fans will cool down the evaporating water and thus keep the water temperature under control on the surface of the tank. Once the surface temperature is cool and water circulates, your tank will have perfect water temperature . Fans comes with one single blade or even multiple blades.All Rights Reserved