Freshwater Aquarium Temperature Considerations

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So you’ve setup your tank, the filter is working and you’ve checked the water ph. Now you need to set your freshwater aquarium temperature with the heater thermostat. What temperature should that be? The answer is that most tropical aquariums do best between 73 and 82 degrees Fahrenheit (23 to 28 Celsius). What you actually set the temperature at will depend upon whether you live in a warm or cool climate. The reason is that you want to avoid water temperature fluctuations as much as possible. Thus if you live in a cool climate you should set the thermostat at about 75 degrees Fahrenheit whereas in a warm climate you might want to set it at about 80 degrees Fahrenheit. This means that the impact of the ambient freshwater aquarium temperature changes will be less dramatic on the tank water temperature.

You should bear in mind that the warmer the water the less oxygen it can hold and therefore higher levels of aeration should be employed. It is also worth mentioning that an acrylic tank is a much better insulator than a glass tank and a reasonable tight fitting lid will also help.

To a large extent the actual freshwater aquarium temperature that you set is not too important, it is sudden changes in water temperature that will kill fish. Sudden changes in less than 24 hours are very stressful to the fish and if it does not kill them it is likely to put them in a poor state of health and make them susceptible to disease. Sudden freshwater aquarium temperature changes usually bring on the ‘shakes’ or ‘shimmies’, ‘Ichthyophthirius’ (ick), fungus or a general decline downhill.

The required heater size (in watts) will depend upon how many gallons of water that needs to be heated and the temperature difference between the room and the water. As a general rule you need 2 watts for raising each gallon of water 5 degrees above surrounding temperature. Large tanks with high required temperature differentials may need two heaters. If so, these should be placed at each end of the aquarium.

You should not have a larger wattage heater than as calculated above. There are two reasons for this; firstly, you do not want the effect of the heater as it cycles with the thermostat to cause a rapid rise in temperature of the water and secondly, if the thermostat should fail you do not want the fish to fry.

What kinds of heaters are there?

There are three kinds of heater, all work well.

• Immersible heaters are the most common mainly because they are easily found and inexpensive. They hang onto the back or side of the aquarium, dangling into the water. A temperature control knob is kept above the water. Their downside is that they can be considered an eyesore and a lot of people prefer the heater to be hidden.
• Submersible heaters as the name implies can be completely submerged in the aquarium. The good thing about these is that they can be hidden behind rocks and plants. These types of heaters are more reliable and can easily maintain a more consistent temperature in your tank. They’re easy to use, slim–so that you don’t notice them as much, and relatively inexpensive although they generally cost more than the immersible variety.
• Filter heaters are a really nice option to consider to maintain an even fresshwater aquarium temperature. They heat the water as it moves through a filter. They are more expensive than other heaters, but they are filter units as well. The big plus of this type of heater is that it is outside your aquarium, so it doesn’t take up space inside and you don’t see it at all!

One final word, make sure you have a good thermometer in your tank. Initially you should check that it is calibrated correctly. After that you should check the reading every day on a regular basis. The best time is to glance at it as you feed your fish. That way you will be aware of any freshwater aquarium temperature problems before they have a chance of affecting the long term health of your fish.

So there you are. Depending on where you live your freshwater aquarium temperature should be set appropriately and should be tightly controlled by a combination of heaters and a thermostat. The actual freshwater aquarium temperature is not so important as keeping it stable.

Bear in mind that the temperature of your aquarium is just one of the things that you need to consider when setting up your aquarium. Good filtration, water chemistry and regular maintenance are all essential if you want to keep your fish healthy.