Fish are cold bloodied which means that they cannot independently control the temperature of their own bodies. It is the temperature of their freshwater aquarium tank. With some exceptions, fish prefer temperatures in the region of 73 to 82 degrees Fahrenheit (23 to 28 Celsius). The particular temperature is not so important. Rapid temperature variations are what cause them problems.
Temperature changes stress out a fish and cause it a great deal of distress. At worst fish can die from this and the least consequence is that they are weakened and prone to disease. Avoid sudden changes in less than 24 hours.
While the exact temperature does not greatly matter to the fish it is something you should think about. If you live in a warm climate then you should set the tank thermostat a little higher than if you live in a cool climate. As a result the heater does not need to work too hard to keep the set temperature. By setting the tank temperature close to the room ambient temperature it will be less susceptible to variation. It might be necessary to increase aeration since warmer water cannot hold as much oxygen as cooler water.
Place your tank away from drafts,sunlight and radiators. In an ideal world your tank should be placed in a fixed temperature enclosure. Glass is not as good an insulator as acrylic.
A thermostat works as an automatic switch simply turning the heater on and off according to temperature requirements. If the set temperature is very different from ambient temperature, the tank temperature will constantly be cycling up and down.
This naturally introduces the subject of heater size. The heater size is a compromise between its ability to maintain the set temperature and it not causing a rapid temperature rise.
There is another reason why your heater should not be too large. That is if the thermostat goes wrong and fails to turn the heater off at the right moment your fish could be fried within a few hours before you have had a chance to notice the temperature rise. This is also a good reason to have a temperature alarm fitted.
These are the recommended heater sizes.
5 to 8 galls – 25W
9 to 20 galls – 50W
21 to 30 galls – 75W
31 to 40 galls – 100W
41 to 60 gals – 150W
61 to 70 galls – 200W
71+ galls – 250W plus possibly additional heaters
If the ambient temperature is less than 68 degrees Fahrenheit you should consider moving up a heater size. Much higher, consider moving down a heater size~Reduce the heater size if it is much higher~Down a heater size if it is much higher}~Maybe go down a heater size if it is much higher~Think about reducing the heater size if it is much higher~Down a heater size if it is much higher}.
. As you probably know, heat travels through a liquid by convection. Convection is the process where hot liquid being less dense than cooler liquid surrounding rises to the surface and cold liquid being more dense falls to the bottom. As a result the heater should be placed centrally at the bottom of the tank in order to help the convection process.
There is a very good heater which is built into the freshwater aquarium filter system on the water inlet or outlet of the filter. The water is heated as it passes through the filter so the heat is distributed evenly throughout the tank. This makes sure that hot and cold spots in the tank do not exist.
So that's it, to avoid many of the problems that freshwater aquarium enthusiasts face avoid rapid freshwater aquarium temperature changes.