Product review (5 stars): Works great on steam humidifier
I have a small one and a half gallon steam humidifier for my bedroom and it always built up a thick layer of scale on the heating element that I had to soak with vinegar to remove every few days. Holmes Lime Scale Treatment Solution kept the scale from forming so all I had to do was add water when it needed it, though you do have to add the Holmes every time you add additional water, and you have to experiment with how much solution you actually need for your water.  I still took the humidifier apart and cleaned it every week or two, but the Holmes made it a lot easier. I would definitely recommend Holmes Lime Scale Treatment for steam humidifiers.