Temperature Diseases

From The Aquarium Wiki
Jump to: navigation, search

About Temperature Diseases[edit]

Temperature diseases are often overlooked. All species of life have a natural band of temperature that they can live in and if we mix different species of fish in our tank then an average temperature is often set. Typically 25°C (77°F) for tropical fish.

Most animals we place in tank are unable to set their own metabolic rate and use the surrounding water temperature to do this.

However a unsuitable temperature over a long period of time can cause the animal serious problems.

Low Temperature[edit]

The animal becomes lethargic and stops moving, it may rest on the bottom. At very low temperatures brain and body functions will slow until the animal slips into a coma or ceases. It will no longer be able to control its movement and may look like it is dead as it simply floats along with the current. If left for more than a few minutes it will die from lack of oxygen.

  • If the animal is kept at its lower end of its temperature band then its growth will be slower and its immune system may be impaired.


  • Heater has stopped working
  • Water change with cold water
  • Room temperature has dropped


Increase the water temperature to at least 18°C (64.4°F) and then slowly increase the temperature to prevent further temperature shock.

High Temperature[edit]

Water can only contain a certain amount of dissolved oxygen in it and this amount varies by the temperature of the water. Warm water hold less oxygen so the animal may be breathing rapidly and will try to swim at the water line as there is a thin band of higher oxygenated water at the surface. Often this exhausts the fish and so it drowns after a while.

  • Note this behaviour often goes unnoticed as it is worst in the middle of the night when the level of oxygen is at its lowest and the owner never sees the fish fighting for their life each night until it dies from prolong periods of Hypoxia (oxygen starvation).


  • Room temperature too high.
  • Heater has become stuck on.
  • Species isn't adapted to live at this temperature.


  • Lower the room temperature and switch off the aquarium lights.
  • Operate a fan onto the tank or water surface to cool it.
  • Switch off heater and examine to see if it is faulty.
  • Replace some of the water with cool water.
  • Add ice or frozen ice coolers from the freezer to lower the temperature.
  • Aerate the water to increase oxygen content.
  • Add a chiller device to lower the temperature.


The use of two heaters, each half the wattage required to heat the tank will prevent over heating if one heater becomes stuck on or conversely if one heater becomes stuck off then there will still be one heater working to keep the tank from cooling quickly.

  • It is recommended to use a electronic thermometer which has an alarm facility if the temperature drops of rises outside the set range.

Temperature shock[edit]

A sudden change of the water temperature can often prove fatal to fish, especially small fish or fry. In general it is the drop in temperature that is more common than a rise and more likely to kill the animal.


When purchasing fish ensure the shop staff adequately insulate the fish bag with layers of paper or plastic foam. The sudden drop, especially in winter time can easily kill an unprotected bag.

Other causes can be water changes with too cold or too hot water. Whilst different species have different tolerances to shock, it is best to keep sudden temperature shifts within 5°C (8°F) degrees if at all possible.