Product review (3 stars): My error. I bought a two-pack from Amazon in ...
My error.  I bought a two-pack from Amazon in 2015 for $16.xx.  Went back into orders, hit "buy again" and went ahead and bought this without reading.  A one-pack for $23.xx. And this is darker than the one I pulled out of the humidifier.  Hmmmmm.....

From now on going to do research rather than rely on Amazon.