One other idea for the future or anyone else with this problem. Pour hot (not quite boiling) water into Nalgene type water bottles and float them in your sump (and change as needed). In theory this should be better/easier to manage than adding hot water directly to the tank.
Side note - I do this for my wife when we camp. Before bed heat some water, put it in a nalgene and toss that in the bottom of her sleeping bag. A simple, safe heater. Happy wife, happy life.