Product review (5 stars): works great for me
I've been using these for years. I use reverse osmosis water in my humidifier (which stops the crust from the hard water building up on the filters), but I has an issue with water/filter turning pink.

I found the Protec cartridges suggested somewhere, and gave them a try.

If I remember to swap them out every month I can generally get 2 (something 3 months) out of a filter (with the water and filter remaining relatively clean).