I am setting up a new tropical tank. I do not want to make 2 trips to the lfs. (tank is already cycled) When I go next time I will be buying fish and a heater. I want the temp of the water to be good for the fish when i bring them home. and then I will put the heater in. all i need is and idea of how i can temporarily get the tank heated up. (room temp is 69~70F)