Product review (3 stars): Not cool. I used them specifically for the humidifier pictured ...
Stains the inside of the humidifiers yellow. Cannot remove stain. Not cool. I used them specifically for the humidifier pictured as well as for evaporating water cycle humidifier. Stained both. Cannot tell if they stained inside of other 2 blue containers. Found them at the local big box store for less than 5 dollars too.