just for your information.
A general rule of thumb when it comes to heaters, for every litre of water you need at least 1 watt of heater.
For example, a 10 gal / 40 litre tank requires a 40 watt heater but manufactureres do not make them in 40 watts, so therefore a 50 watt is perfect for a 10 gal / 40 litre tank.
Always worth getting the next sized up heater for your tank, 100 litre tank, get a 125 or a 150 watt heater, this helps to ensure the heater does not have to work continously to maintain the desired water temperature thus helping with longivity of the heater as well as helping keep your electricity costs down a little bit less.
Adjustable thermostatic heaters tend to come in 25, 50 , 75, 100 watts sizes and so on and so forth.
Smaller heaters such a 10 watts tend to be fixed temperature ones at around 24C.
Having 2 heaters is worth doing only in larger tanks say 4 foot + long tanks as having a heater at each end of the tank will help to ensure all the tank water is maintained at a even temperature throughout. Would not bother having 2 heaters in a 10 gal tank, a bit overkill but won't do much harm really.
I always say the less electricial things in the tank, the better, helps to keep the tank looking tidier as well as a little more safer
