Product review (1 stars): Caused breathing issues!
I don't know what chemicals they put in these tablet (since no ingredients are listed), but these guys caused some major respiratory issues for my husband and me.  The tablets work in that they do reduce the hard water dust that comes out of the humidifier, but waking up with tightness in my chest and throat is not worth it.  My husband was getting over a respiratory infection and I thought the humidifier would be soothing since the air has been so dry.  He woke up short of breath, coughing and hacking like he was getting sick all over again.  I left the windows open and did not use the humidifier the next night and he felt like himself again.  Buyer be ware!