I have never used a hydrometer in my incubator. If you have condensation on the sides and your temps are right you are probably pretty much saturated. That said, I live in florida and the humidity here is generally not a problem period. I keep a water bowl on top of my heat tape in the incubator also to saturate the air around the tubs also but the heat tape does not kick on too often this time of year. I have to cool more than heat.