Actually, the most often stated "desired" humidity, that I have seen, is around 50-60% for wine. The lower end for the labels and the upper for the corks. I try for the upper end, but then I'm also storing cigars, where 70% is an ideal. To get to a balance, so as not to introduce mold on labels, I just have a humidor for the cigars. However, in AZ, the instant that I bring the stoogies out from their home, they dry out, and blow away in the breeze! :-{
As to bringing UP the humidity, it might well be that the cooling/conditioning unit is actually trying to keep the humidity at ~50% and is working a bit harder to remove what is programmed in as excess humidity. My Whisperkool tries for 50%, but I added a small fountain and some splash rocks to nudge it up a bit. When the cellar was new and settling in, I did as you have tried, and placed a large sponge into a dish of water. I found that a towell, half in and half out, did a much better job of raising the humidity.
I hope that others comment on the humidity issue, as all I have to go on is some very general reading, and there only seem to be warnings about dry corks if too low, and moldy labels if too high.
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