Product review (1 stars): Bad smell at first, growing mold within a week despite aggressive prevention
For years, I've had the formula for long lasting humidifier filters without discoloration, mold, mildew, etc.  Ever since developing the routine I describe below, my filters have lasted a long time, even a whole season at times, and while stiffening after a long while, rarely discolor until after months of use, and only slightly.

I use fresh water every night with a silver Protec drop in I change every month, empty the water vessel every morning and allow the fan to completely dry the filter and its well all day long before refilling at night.  I always bleach both the filter tray and container weekly before refilling.

This routine has kept all my filters clean, fresh and not discolored for years now.  Until I bought these. The first time I put one in, there was a horrid fish smell that lasted hours.  That should have been my first hint that these are not like all the non fish scented filters I've used before.

Now, after only about a week of actual use (we've had some mild winter nights, so no humidification needed)I took the unit apart for its second cleaning since putting in the new filter and the whole bottom of it is deeply rust colored.  I don't have rusty water in my home, and nothing here ever gets rust stained, not sinks, tubs, clothing, etc.

Further, the way I know there's mold buildup is how itchy my eyes get and it goes away as soon as I bleach the unit out.  With the old filters, that has never happened before a week's time, but I've had to bleach the unit twice as often due to severe allergic reactions since using this filter.  Not only is it not anti microbial, it's apparently extremely efficient at growing mold.  Cleaning it stops the allergy symptoms.  These filters not only don't last long, they appear to be a very efficient medium for growing stuff that's harmful to your health.