A heater can raise the temperature of a fish tank if needed
Degrees Centigrade.
Betta fish will not be harmed if they are in a filtered tank. If the new tank is about the same size as the old tank you should use the old water or most of it in the new tank. If the new tank is larger so you have to add lots of new water then you should fill the new tank with the new water and let it sit (preferably with the filter running) for two or three days before adding the fish. Also when you move the fish make sure the new tank is at the same temperature as the old tank.
You should have a thermostatically controlled aquarium heater, and a good thermometer to monitor the temperature. Although they are sold, don't use the type of thermometer that you stick to the glass; that doesn't give you an accurate temperature. Use one that goes in the tank itself. For tropical fish, I have had the best success with the temperature about 75-78 degrees F.
Use the Thermostat
no because if its a freshwater tank the rain has salt in it
The mass of a fish tank should be measured in kilograms.
depends on the size of the fish, there might not be enough oxigen in a small fish tank.
The simple answer is yes.
math
Of course you can.
It will either have to get used to it or die.
no