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Question: What is the correct temperature for my aquarium?

Answer: What ever suits your fish..

Please don't take this as a flippant reply, it is in fact the only correct answer, although I will expand it a little to suggest around the mid 20s°C. In the wild fish are found in water temperatures ranging from minus 1 - 2°C, (remember Sea Water does not freeze at 0°C), to the outflows from Hot Springs at possibly 40 - 50°C. True, these examples are at the extremes, but there is a vast range in between, so in general terms, what we call "Cold water Fish", like temperatures 10 - 20°C, and "Tropical Fish" 20 - 30°C

All fish are ectotherms, usually called Cold-Blooded, but actually means receiving their body heat from the outside environment, and as such, vary their metabolism according to temperature, the hotter they get the more active they are. Even cold water fish such as Goldfish and Koi will virtually "Shut-down" if the temperature falls much below 10 - 12°C as happens in ponds during British winters. Most Koi and outdoor Goldfish in the UK don't take any food between the end of October and mid March off the following year. This is in sharp contrast to their likely birthplace.. many commercially bred Koi and Fancy Goldfish are from Israel and Malaysia where breeding temperatures are around the low 30s°C. For most aquarists however the best temperature for cold water species is around 18 - 20°C.

White Cloud Mountain Minnow"Tropical" species have an equally wide range, from the steaming pools in a Peruvian jungle where water temperature can reach 38°C, to the White Cloud Mountains in northern China, home of the White Cloud Mountain Minnow, and where mountain streams can be as cold as 5°C.

While I would not suggest keeping your White Clouds at this temperature, I have successfully breed this species in a totally unheated tank in a garden shed. Actually I shouldn't claim any credit, the White Clouds bred all by themselves. They will in fact lose their colour if the temperature rises too high, above 26°C. Plates are also a mountain species found in Central America and Mexico and well able to handle temperatures in the mid to high teens. Discus on the other hand really love the heat, 30°C and above is a must for these beautiful South American Cichlids.

So as I said at the start, there is no "Correct" temperature, each species has it's own preferences and all we can hope to achieve for a community tank is a compromise, and that is likely to be around the mid 20s°C.

Just as a little byline, the term Tropical (as defined by the Köppen climate classification, named after its Russian inventor Wladimir Peter Köppen (1846 - 1940)), is a habitat were the annual mean temperature is above 18°C.


Maroon Clownfish in an Anemone