The majority of aquarium fish, both freshwater and marine, hail from the tropics. However, in a heat wave or under the light of high-powered aquarium lighting you can heat aquarium water beyond safe temperatures. When aquarium water gets above 82 degrees Fahrenheit, you need to take steps to cool the water. Aquarium chillers work well but cost hundreds of dollars. For temporary cooling, you can use one of several techniques.
Issues With Overheating
Overheating causes several problems for fish and other aquarium pets. All fish and invertebrates have adapted to the temperatures of their home waters. When water heats beyond these parameters, fish begin to struggle. They have no means of cooling themselves down, and their bodies cannot function normally. Heat causes stress and lowers the amount of oxygen water can hold. The same problems hold true for aquarium inverts.
One quick way to reduce temperature is to cut off the lighting. If you have an aquarium that features only fish or non-photosynthetic organisms like crustaceans, you can completely turn off the lights until the tank cools. However, a lack of light can kill plants or coral. Compromise by shortening the amount of time per day they get light, cutting down to eight hours. You can also select types of lighting equipment that produce less heat, like LED arrays.
Fans can also cool aquariums. Some equipment, like certain high-output lights, often have fans incorporated into their fixtures. You can use a desk or window fan to cool the aquarium. Just run the fan over the water. Always use the lowest setting to avoid blowing water out of the aquarium.
You can also use frozen water bottles to cool down. To make this work, fill a sterile bottle three-quarters full of water and freeze it with the cap off. Once the water has frozen, put the cap back on so the melting water won't alter water chemistry. You need to experiment to figure out how many bottles it takes to cool your aquarium. This method cools the water quickly, and you need to keep an eye on the water temperature. Avoid changing temperature more than three degrees Fahrenheit. Sudden changes in water temperature, even toward ideal conditions, stress fish out.