Gen, if it's 68-70 at night, you might try just draping a towel or something similar over the tank to insultate it slightly and retain a little more of the heat. Alternatively, you could just bump the heat on the heating pad back up that half notch around the time it gets dark outside. 74 is a little cool, but it's nothing to stress about for a night temp on the cool side. a little experimentation and you should be able to get it back up 3 or 4 degrees.