Have you calibrated your hygrometer so you know how accurate it is? I’ll throw in the thermometer one too.
Rebel’s Thermometer Calibration
http://cmfarm.us/ThermometerCalibration.html
Rebel’s Hygrometer Calibration
http://cmfarm.us/HygrometerCalibration.html
Humidity is controlled by the surface area of the water. The more surface area you have the more water can evaporate. How deep the water is has no effect on humidity, just how long that water lasts before it all evaporates. You don’t say if your humidity is too high or too low.
If it is too high, you need to decrease your surface area. I don’t know how you are putting water in there, but either take out a container, a sponge, or whatever it takes. If your water reservoirs are built in, let one go dry. Another trick is to cover part of a reservoir with foil to reduce the surface area.
If you need to increase the humidity add additional water reservoirs. You can put a sponge, paper towel, a piece of towel, something like that touching water in a reservoir so it draws water and gives more area for the water to evaporate from but remember that will dry out the reservoir faster.