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Aquarium guides/Keeping an aquarium cool in summer

Keeping an aquarium cool in summer

Warm water holds less oxygen, so a tank creeping above about 82 °F stresses most fish. Cool it by running the lights less, opening the lid, pointing a fan across the surface and adding surface movement; float sealed bottles of cold water for quick help, a few degrees at a time.

A planted freshwater tank
Shown: a planted freshwater tank. Photo: Xema Romero, CC BY-SA 3.0, via Wikimedia Commons

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Signs of heat stress

Fish gasping at the surface or breathing fast, a thermometer reading above the species' range, cloudy water from a bacterial bloom. Cold-water fish such as goldfish and white clouds suffer first. Gasping fish.

How to cool it

  • Turn off or shorten the lights and close the curtains.
  • Open the lid and point a fan across the water: evaporation cools it (top up with dechlorinated water).
  • Add an air stone or point the filter outlet at the surface.
  • Float sealed bottles of cold water; avoid ice straight into the tank and drops of more than a few degrees.
  • Unplug the heater if the room stays warm.

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