Product review (3 stars): Reviving old filters
When these filters became virtually unavailable a few years back I tried soaking the old one one I had in vinegar every time I did a major cleaning of the humidifier, on the theory that the vinegar will reinvigorate the filter by dissolving the minerals which have been captured by the filter. It seems to work - we have had no white dust problems with the filters so treated, and have so cleaned that one filter several dozen times now.