Product review (2 stars): Doesn't seem to work at recommended strength
I bought this to use in a brand-new Honeywell QuietCare humidifier.  Using it at the rated strength of one lid full of solution per gallon of water, I was unpleasantly surprised to discover that my new humidifier's evaporation chamber had orange organic muck in it within the first 4 days of continual use.  Admittedly, I have hard water and was prepared to see white crust or scale (at least on the filter), but this kind of organic growth is what I understand this water treatment is supposed to inhibit or prevent!  By trial and error I discovered that the it requires about TWICE the manufacturer's suggested rate of solution to keep my water clean.  I suspect I'll go through a full bottle in a month of use, and I'm not sure its worthwhile, compared to simply cleaning the tank and rinsing the filter periodically.

I'd echo the other review comments that, if you are refilling a partially drained tank, you will get a lot of foaming if you add the BT treatment before the water, rather than filling the tank nearly to the brim and topping off with the capful or two of solution-- although, to be fair, the foam subsides quickly (within a minute or so) if you accidentally reverse the order.

On balance, I'm not sure that this Treatment is a cost-effective add-on for evaporative humidifiers.