Product review (5 stars): You only use a capful for each tank of water ...
You only use a capful for each tank of water, so it lasts a long time, and I assume it is helping to keep my humidifier from getting gunked up, because it's a clean machine.  I also use the Baceriostat, which creates some foam (I patiently wait for the bubbles to die down before filling).  The caps are different sizes, but I assume that is for a reason.

I came back to clarify that because the cap for the Lime control solution is bigger than the Bacteriostat, I've been using slightly less than a full capful so I don't run low prematurely.  I have a water softener, so I didn't expect to have much trouble with scale, but after a month, I can say the unit remains clean as a whistle. It's not expensive for what you get - this should be enough to last all winter.  Another tip is to add the Bacteriostat after you start adding water - when the tank is already nearly full - to reduce the amount of suds (it gets VERY sudsy otherwise and you have to wait until they break up before you can fill the tank completely and close it up.