The Humidikit comes with a 1-L bottle, would using a 2-L pop bottle instead cause damage to the ultrasonic disk?

We do not recommend a bottle larger than one liter because it can cause a couple issues. One being that it can harm the ultrasonic disc. Another issue is the oversize water bottle cannot support itself and cause spillage. This water on the outside of the unit can cause shorts and damage the humidikit.