I just fill the trays and when they are empty I fill them again. I have try to keep they fill all the the time and ended up not have enough evaporation. Think of it as a hen on them. She will get up and the humidity will go down the only big concern is to keep water in them and have them full when it is lock down. You need to let some of the water evaporate. Have you check the humidity gauge. Put it in a bag with a cup of salt water. Leave it for 24 hrs and it should be at 75% if not note how much it is of and then you will know the humidity in the incubator. Also have you calibrated you thermometer? You need one that will go to 32 deg. Get a cup of crush ice and put some water in it to make a slush. Then put the thermometer in it and it should go to 32 if not note how much it is off and that is where the temp needs to be. This comes from many bad experience not knowing. Also the water needs to have 2 tab of bleach to 1 gal of water. This help keep the bacteria down in the incubator.