Product review (5 stars): Really works!  No growth on my wick filter any more!
Like everyone else I have a Vornada evaporative humidifier that basically uses a wick filter that soaks up water and holds it until the fan on top sucks it and circulates it into the room.  Problem is, the wick retains the water so when it's off the water on the wick is prime breeding ground for growth of bacteria mildew and other nasty stuff.  I had to change my filter almost weekly!!

So I put a capful of this bacteriostat for every gallon of tap water (New York city water: not particularly hard or soft) after filling up my tank.  It doesn't have any noticeable smell.  But wow, I have now gone about 2 months (that's 8 weeks!!) without having to change my filter and I didn't even clean my tank either just to experiment.  No growth or smell nothing nasty in my dehumifier that used to require weekly filter change and clearing.  Amazing...

I just wanted to see how long I could go without changing/cleaning but I wouldn't recommend not cleaning for two months haha.  But it looks like I can go longer...!

3/22/2014 Edit:  I am still on my first set of wick filters and although it doesn't smell bad, the top 1/2 inch has now turned a bit brown.  So I have gone almost FOUR months without ever cleaning the humidifier or changing the wick.  Just simply putting a capful for every gallon of tap water and away I go.  W.O.W.  I am just flabbergasted at how well this thing works!  I used to change my wick EVERY WEEK (5-7 days) with weekly cleanings.  I just went 4 months, folks...