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How to Keep Your Aquarium Cool in Summer Heat

Aqueon Live Fish Tank in Living Room

Most of us enjoy the warmth of summer, but if you own an aquarium and don’t have air-conditioning, prolonged periods of extreme heat can be harmful, if not disastrous. The effects of rising temperature for fish are different for each aquarium and vary depending on tank size, depth and surface area of the aquarium, fish population, water quality, circulation and surface agitation, and ambient room temperature. Short heat spells are usually no cause for panic, but the warmer the weather and the longer it lasts, the more problematic it can be.

How Fish React to Changes in Water Temperature

While some fish like Discus, Clown Loaches, Bettas and Rams thrive at temperatures in the mid to upper 80’s, most tropical fish prefer 74° to 80° F, common goldfish do best at 60° to 70°F, and fancy goldfish should be kept between 68°and 74°F. As water temperature rises, a fish’s metabolic rate and activity level increase, which means it needs more oxygen. In turn, the ability of water to hold dissolved oxygen drops with rising temperature, creating double jeopardy for our watery pets. The problem is even more serious for marine creatures because saltwater holds less oxygen than freshwater of the same temperature. Make sure you have an accurate thermometer on your aquarium and keep an eye on it as the weather heats up.

Signs of Stressed Fish During Hot Weather

The first sign of stress to your fish during hot weather is rapid gill movement or gasping for air at the surface. Corals and anemones will close up and their polyps or tentacles will retract. Algae growth may increase, and the water may begin to turn cloudy due to a bloom of heterotrophic bacteria. When your fish are stressed, their immune systems are compromised and they’re more likely to get sick. In severe cases, your filtration system may not function as efficiently and toxic ammonia and nitrite levels may begin to rise.

How to Prevent Your Aquarium From Overheating

There are a few simple things you can do to prevent your aquarium from overheating, or cool down aquarium water in summer.

  • Install an aerator to improve gas exchange at the surface and maximize the dissolved oxygen content in the water.
  • Open the aquarium cover and position a fan to blow across the surface of the water. (You may want to lower the water level an inch or two to prevent fish from jumping out.) This is especially effective when combined with the use of an aerator.
  • Float a bag of ice or cold water in the fish tank to gently lower the water temperature. (Take care not to lower the temperature more than 2 or 3 degrees F in a 4-hour period.) Avoid putting ice cubes directly into your aquarium unless you make them with reverse osmosis or dechlorinated water.
  • Perform small partial water changes with slightly cooler water, making sure not to drop the temperature of your aquarium too rapidly.
  • Turn your heater down, but not off. Some experts suggest unplugging the heater, but the risk in doing that is the ambient temperature suddenly dropping and forgetting to plug it back in. A sudden drastic drop in aquarium temperature can trigger the onset of ich or other parasites.
  • Turn off the aquarium light – or in the case of planted and reef aquariums, limit the number of hours the light is on – to help reduce heat generation.
  • If your aquarium is near a window, close the curtains to prevent direct sunlight from heating the water.
  • Install a chiller on your aquarium in a well-ventilated space. This will help keep your aquarium at a constant temperature, no matter how hot the weather gets!

    Regardless of what methods you choose to prevent your fish tank from overheating, always remember to make any fish temperature changes in your aquarium gradual.

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