It looks like the accurites are right beside the water, nearly touching. That probably doesn't give an accurate reading for what the humidity is in the entire tub. Have you tried repositioning the accurites to see if you get similar readings at the other end of the tub for instance?

Also, are you using the min/max feature on the accurite? If the fan is causing problems, you will probably find that your temps & humidity vary not only from tub to tub, but within a single tub over a few hours.

I'm really just guessing since I have no experience with a rack, but I have noticed that if the humidity meter is too close to something wet, it spikes up more than if it is across the enclosure.