losing humidity?

so im losing a lot of humidity from my egg boxes, i use a ralph davis style plastic tub with a sheet of plastic across the top under the lid, i did the same last year and it worked great, but this year i have two egg boxes both losing humidity and in fact i coulndt seem to get it over 85% from the start! im using the same vermiculite as last year! and i open the tubs once every other day to vent them, any ideas why its doing this!!!
thanks

Could be that the ambient humidity outside the tubs and in the general air is lower than usual. You could put a bowl of water inside the egg boxes which won't tip over to help up the humidity, or you could put one in the incubator to try and raise the ambient humidity, to see if that would help. Otherwise, I can't imagine why it's not working this time around! Maybe the plastic isn't sealed well enough???