This? http://www.amazon.com/Zilla-R-Zilla-.../dp/B0043XHZJ4

Those can still be off, as can Accurites. I'm just having a hard time believing your humidity is low in Seattle, so my first suspect is the hygrometer. There is a way to test it though, Google the hygrometer salt test.

If your hygrometer is right, I'd consider switching to a tub set-up. Details of which you can find here.