The temp here is about 4*C today! My heaters just can't keep up so I'm doing everything from wrapping tanks in blankets to turning all the lights on and covering the top of the tanks (wich seems to work on my 70 gallon, although it looks like a pink floyd show) I was wondering, I heat my water for the house with an instant hot water heater (LNG fire) but the heat exchanger looks to be aluminium or some other grey metal. do you think if I did warm water changes from there would it be safe? or would I be better to heat some water on the cook top?