You would think with surface size of water not changing there wouldn’t be an increase in humidity. Today it would be as high as 57 so I opened the vent more as RaineyTN suggested and then it would go down. I don’t understand how more water is causing this to happen but I don’t know what else it could be. Good thing is opening the vent works.I always fill mine all the way, I don't see any reason why it would benefit the hatch in any way to only partially fill it so I don't know what to say about that suggestion. All I can say is that I've had great successes with my hatches and I do fill it.
Humidity will evaporate from the surface of the water so the surface size doesn't change when you fill side A, it just takes longer to evaporate because it's deeper.