Comin in a little late on this thread but I thought I'd add my

I just picekd up a Hygro. today and I put it in and it said my humidity level was at 40 . So, after reading on here of course, I to a towel nice and wet (well not too wet mor elike a little damp) and laid it over about 2/3, maybe a little less, of the tank. I checked the hygro. about 20 mins later and it was up to 50%.