Product review (5 stars): works but still need the liquid to control algae and bacteria to lengthen the use
This filter works just fine, but I've found with any filter, to SAFELY extend the life of the filter, you must also purchase and use a liquid (humidifier bacteriostat) made to use in conjunction with humidifiers which will prevent/ reduce the algae and bacteria.  Otherwise, if you use your humidifier as much as I do in the winter, and do not add the liquid, the filter usually needs to be changed after 2-3 weeks.