I too live in Ohio and have an unheated garage. I'm just getting started with discus (in fact I'm just cycling the 75 gallon tank and don't have any fish at this time). I've got a 55gallon plastic drum that I'm keeping in the garage and using to prep water for the tank. I've filled and am using an Fluval E300 watt heater to warm it to 80 degrees. So far no problem.