Product review (4 stars): Works, Not that harsh
I found some of the lower ratings for this product terrifying!  I didn't notice them until I had already placed the order (><), and probably would not have ordered it if I had seen them earlier.  HOWEVER, I used this product without rubber gloves and would describe it as "mildly acidic".  Its not a terribly concentrated harsh chemical, but it is harsher than regular household cleaners.

Now, that being said, why would you want a chemical water treatment?  Two words: Legionnaires' disease, or Legionellosis.  There are things worse than having chemicals in a house, and if you have a household humidifier, especially a larger one, please be careful to prevent bacterial growth.