trying to regulate humidity in incubator

Help! I bought a thermometer/hygrometer this year to try and get a better hatch. My temperature has been consistent but the humidity % has large ranges (often from 37%-60% or 44%-60%. It's even gone as low as 17%). I find that I am adding very small amounts of water every day, sometimes a couple times a day in order to keep it at the 50-55% range. I also keep socks of rice in there so it doesn't spike far over 60%. I felt it was regulated before adding the eggs, but since adding the eggs it seems to be all over the board in %. I notice over night is when it gets the lowest. (these are in my classroom). Should I take the socks out before going home at end of day? Any other suggestions to help it regulate more? I worry about a low hatch. We are currently on day 10 in the incubator.