Either a bad reading or you have forced air heat and a lot of air exchange sucking out all the moisture you just added. I have the same model in a medium sized

Either a bad reading or you have forced air heat and a lot of air exchange sucking out all the moisture you just added. I have the same model in a medium sized room, with the hygrometer on the other end of the room where it is open to the rest of the house and the second floor. About 3/4 of a tank yesterday bumped us from about 17% humidity to 22%, with a fire going in the fireplace.