Most tropical and Saltwater Fish will like a temperature of 78 degrees to 82 degrees. Goldfish will appreciate temperatures a little lower than this.
All depends upon the Species you intend to house/keep in there.
This can be as low as 65F through to 75F as it will depend on what is best for the particular cold water fish you are keeping
So you can make sure the fish has a suitable temperature
A heater can raise the temperature of a fish tank if needed
a big fish tank .
about 85F
Any tank under 10 gallons is not suitable for fish, but you can have perhaps a few ghost shrimp, or use it for live plants
Normal tropical fish tank temperature; 77F-82F
You should add cycle a chemical to make your tank suitable for fish than buy a fish or get one then put it in a bag for 30 min. and every 10 min. add water from your fish tank to the bag than after 30 min. release you fish.
Inside the tank as it is for you to see the water temperature.
Yes it is important to have a thermometer in your fish tank. The temperature of the water should be between 75-80 degrees.
It is used to regulate the temperature of the water
The instrument that is needed to measure the temperature of the water is called an "Aquarium Thermometer".
If the temperature is around 20 degrees (Celcius) probably not. But for a five GALLON fish tank, probably.