Quote Originally Posted by wolfracer
Quote Originally Posted by badflash
A hot water heater with a circulating pump an a heat transfer coil can work too. Small appartment heaters put out lots of heat.
That is actually my original and current plan, but I thought if there was a multi-fuel solution it would be worth looking at.
I believe water heater have, or use to have, a zinc anode in them to prevent or minimize electrolysis. I am not sure if that would effect fish, but that is why it is not recomended to drink hot tap water (or at least it used to be). Maybe newer water heaters are different. I would look into that before trying it.

From wikipedia "Other examples of protection by use of sacrificial anodes include protection of voids in the glass lining of mild steel water heater tanks via use of magnesium or aluminum alloy anodes,[1] protection of off-shore oil rigs via special alloy anodes for use in salt water, protection of lock gates in water ways, etc." see: http://en.wikipedia.org/wiki/Sacrificial_anode