If you are holding steady at 40%, live with it. But don't worry if it starts to go down, let it. Then when it gets to 25%, add a LITTLE (1 oz.) of water. This should hold it at the right level of humidity. Then on day 18 kick it in the pants and bring it up to 60%. Mother Nature will take care of the rest. It is better to be a little low on the humidity than high, if it gets to high the chicks will drown. To low and the chicks have a hard time hatching. If this happens and you need to help a chick, place a moist tissue next to it. DO NOT TRY TO PEEL THE SHELL OFF. This will cause the chick to bleed.