Mike hit it right on the nose. Condensation forms due to the difference in temperature inside the egg box and outside the eggbox. Get the temperature in the incubator where you want it and after a while the temperatures in the eggboxes will stabilize and match it. That's why it's recommended to have your incubator up running for at least a few weeks before you get eggs. It can sometimes take a day or two for the temperatures to all sync up and stabilize.