As the Jobo rotates, it touches the water which is set at 75F. I would imagine it's because of the hot weather which will allow the tank to create a humid environment within in the tank. I do know that on colder days, I would have to set my temperature to around 75.7F or 75.9F to get a perfect 75F in the tank. I just didn't realize how tremendous the effect would be for a hot day. My Tmax negatives ended up with a lot more contrast than I really needed/wanted.