Product review (5 stars): Four months of mold, calcium and lime free goodness in the humidifier.
We have a large Honeywell humidifier (Honeywell QuietCare Humidifier HCM-6009, 9-Gallon) that puts out 9 gallons a day. This is in out office that's on a separate HVAC than the rest of the house - that has a whole house humidifier. Well, the whole house humidifier and our old humidifier suffered from lime and calcium build up. The stuff in a real pain to clean.  There's not much we can do about the whole house one, but we decided to get proactive for the Honeywell.

We have two tanks in the humidifier and have this in the tank we fill most often (four times a day.) It's been a couple of weeks and there's no sign of calcium or lime. Usually the build-up has started by now.

So I have to say it's a winner. Plus with the 60 day life per cartridge means that one set will last you the entire humidifier season (at least in the Midwest.)