Cool the Area

• Keeping the area and room cool where the tank is located will help lower the temperature of the water. Run an A.C. in the room where the aquarium is located. Remove the hood of the tank (you can cover the top with a screen to prevent jumpers) and direct a fan to blow gently over the surface of the water. Turn the tank's lights off during the hottest part of the day, as the lights give off heat. If your equipment is in a cabinet, open the cabinet doors to allow the heat from the pumps to escape.
  
  

Keep Water Moving

• Keep the water moving with a strong pump, and keep it well-aerated with a bubbler. Moving water is cooler than still water, and water with plenty of dissolved oxygen will keep your animals from suffocating on warm days.
  
  

Ice

• One trick some aquarists have used to create an inexpensive "chiller" is to take a small canister filter with the motor on top and immerse the lower half of the canister in a bucket of ice. However, with this method, you run the risk of your temperature fluctuating too much if you use too much ice, or don't replace the ice at the correct interval. In a power-outage or if your chiller breaks down suddenly, you can temporarily float a sealed plastic baggie full of ice in your aquarium. Be certain not to allow your temperature to fluctuate too rapidly, or risk extreme stress to your animals.