How do you decide what size heater to put in your tank? I have heard its better to put 2 or 3 small ones than one big one is that true and why?
I just use one that is the right size for my tank. I do understand why you would put two smaller heaters, you could put one on each side of the tank so that you don't have one side that gets more heat than the other.
5-10 gal 50watt/20-30gal 100watt/55gal 200watt/75 300watt/ not my opinion just what I read off the box.
All depends on what the temperature difference you are trying to overcome.
Heater Guide Example:
If you need to raise the temperature of a 55 gallon tank 15 F, simply use the guide below to find out what wattage is needed. The corresponding wattage is 190 watt, therefore you would select a 200 watt heater. For me, my downstairs theater room may get down to 60 at night for my 75 gallon. Therefore a 300 watt heater is used.