"Set to"? Are you referring to the thermostat or a thermometer that is reading the actual temp? A thermostat setting does not necessarily mean that the inside of the tub is the same temperature, which is why you need the thermostat probe between the tub and heat tape, and a thermometer probe on the inside floor of the tub (or a reliable temp gun to read that spot). You then set the thermostat based on the thermometer reading.