Ive got baby ducks in one in lockdown right now.

I filled both troughs and opened the vent halfway, but the humidity dropped, so I closed the vent back to 1/3rd and its holding steady at 73%.
I talked to a rep for this incubator and he recommended using distilled water in it and not regular water. At night or before I went to work, Id top it off a little because before I did this, Id find the humidity dropped down to as much as 17%!

Since Ive finally figured out the "sweet" spot for humidity, I dont touch it. One us piping now, so I'll see how well this incubator does for its first hatch.