Product review (5 stars): A "Must" for hard water users (with AOS models 7145, 7147).
We have used this in our 2 Air-O-Swiss humidifiers, models 7147&nbsp;<a data-hook="product-link-linked" class="a-link-normal" href="/Air-O-Swiss-AOS-7147-Ultrasonic-Humidifier-Warm-and-Cool-Mist/dp/B004FO9P8U/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Air-O-Swiss AOS 7147 Ultrasonic Humidifier - Warm and Cool Mist</a>&nbsp;& 7145&nbsp;<a data-hook="product-link-linked" class="a-link-normal" href="/Air-O-Swiss-AOS-7145-Ultrasonic-Humidifier-Cool-Mist/dp/B001GSZBEA/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Air-O-Swiss AOS 7145 Ultrasonic Humidifier - Cool Mist</a>&nbsp;for the past 1 and 2 years, respectively. Even though we have a water softening system, it doesn't remove all the hard mineral content from the water; these complete the task. Without these installed in the humidifiers, white mineral dust (including the sodium in softened water) ends up on and about the humidifiers, cleaning of the humidifiers is needed more often and it stands to reason that the life of the humidifier is shortened. These excellent units are expensive, so it makes sense to maintain them properly.

In a normal Wisconsin winter season, a single cartridge has done fine (although the AOS company, of course, recommends changing them more frequently). During a 120-day season, I run these in our bedrooms 70 to 80 days for 8-16 hrs/day. Frequency & runtime depends on outside humidity (or lack thereof) and how often our furnace runs. The only downside I find to using these (cost not considered) is that they reduce, by about a pint, the amount of water you can get into the reservoir, requiring more frequent filling. I just set a morning & evening fill schedule, and all is good.

There are refill packs available (one of which I have), but I haven't yet been able to open a cartridge by season's end. From the reviews I've read on the refill packs, it's worth it to just buy a whole new cartridge. Highly recommended!