Both are plugged into a rectangle extension cord connected to the wall jack. There are 3 switches but neither affect the extension cord, only turns on 3 different lights. The tank is also covered with a hood.
every connection is a place to lose electricity statically. running too much amperage on one line (be it in the wall or just the same breaker) degrades the system over time. if you are or have run too much on the same line it's likely your lines could be creating resistance through degradation or burning electrons through heat. there's a lot to be concerned with. if it's not something that eventually jumps out at you with your tank you might want to consider checking/testing your electrical system in your home for heat generation or power loss especially where it pertains to anything on the same circuit as your heaters.
just another thing to consider that hasn't been mentioned.
Something else that hasn't been mentioned (at least I think it hasn't) is the amount of "work" you're asking the heater to do. How far above room temperature are you asking the heater to take your water? My thermostat is set to 60 degrees on my lower floor, so my heater has to raise the water temperature by about 16 degrees. Quite a bit in my estimation, compared to someone who has their room at 70 degrees. Is this more of an issue for frugal northerners?
Something else that hasn't been mentioned (at least I think it hasn't) is the amount of "work" you're asking the heater to do. How far above room temperature are you asking the heater to take your water? My thermostat is set to 60 degrees on my lower floor, so my heater has to raise the water temperature by about 16 degrees. Quite a bit in my estimation, compared to someone who has their room at 70 degrees. Is this more of an issue for frugal northerners?
Your question hits the nail on the head. The proper way to size a heater is not by using a watts per gallon formula. It's as precise as using inches per gallon as your stocking guide. You need to determine the ambient temp of the room, the volume of the tank, and the desired temp at the very least. http://freshaquarium.about.com/od/heating/a/heatersizeguide.htm
Even this is a bit oversimplified but it's alot better than a watts per gal formula.