What is Temperature?

Temperature is simply enough, the degree of hotness or coldness of the aquarium environment (measured in degrees Farenheit or Celcius).

Goldfish are commonly classified as "coldwater" fish. This can be an often misleading term, as ideal aquarium temperature for goldfish is actually between 70-75^oF (21-24^oC). Goldfish are classified as coldwater fish, because unlike tropicals, they can withstand cooler temperatures. Goldfish can tolerate temperatures ranging from 32-86^oF (0-30^oC).

When it comes to water temperature (as well as most other aspects of water quality), it is best to maintain a stable environment. Sudden temperature fluctuations are very stressfull for your goldfish. For this reason, it is good practice to age your water before adding it to your aquarium and to acclimate new fish to your aquarium (instead of just "dumping" the new fish straight in).

To ensure a stable temperature within your aquarium, an aquarium heater can be used. Choose a heater that has about 3-5 watts per gallon (if you are using 2 or more heaters, use the combined wattage). So if you have a 50 gallon tank, a 250 watt heater OR 2-125 watt heaters should be sufficient. It is also advisable to place your aquarium in an area that will not experience frequent temperature fluctuations: away from main entrance/exit doors, away from radiators/heating vents, away from windows, etc.

You should also have a thermometer to gauge the temperature of the aquarium, in case your heater fails or to alert you during heat spells or cold spells. Aquarium thermometers are either internal (sticks via a suction cup to the inside aquarium wall) or external (an adhesive strip that you stick to the outside of your aquarium wall). The adhesive strip is more convenient, but the internal thermometer gives more accurate temperature readings.

Note also that maintaining a stable temperature will discourage breeding. As instinctively, goldfish are triggered to breed during a gradual warming that follows a prolonged cooler period (ie. simulating the spring/summer following the winter season).