im starting construction on an indoor pond/aquarium in my basement for a host of tropical fish i have that are really large for the aquariums they are currently in. i feel bad for them because they seem so cramped up in these little 90 and 75 gallon aquariums they are in. the project aquarium im building should hold around 360 galllons according to the pond calculator on the internet. my question is has anyone with an indoor pond ever tried using a water bed mattress heater to heat their indoor pond?? i figure if i put it under the liner before i fill it up with water it should work in the same way it does on a water bed Thoughts??