Mineral deposits are hard particles that are best reduced by
softening. It appears that some hardness is getting by your softener,
which is completely normal.
A water softening cartridge can take care of this problem. Here is a
filter cartridge that will reduce hardness.
http://www.waterfilters.net/Pentek/wholehouse/Specialty_Filters/WS-20BB-Water-Filter.htm
You will also need the housing, bracket, and wrench from this page.
http://www.waterfilters.net/culligan/wholehouse/housings/20_BigBlue.htm
If you want a smaller filter to just soften the water to the mister,
then you can use this 10 inch standard size version of the above
filter:
http://www.waterfilters.net/Pentek/wholehouse/Specialty_Filters/WS-10-Water-Filter.htm.
Here is the housing for this filter:
http://www.waterfilters.net/culligan/wholehouse/housings/HF360.htm
If you'd like, you could also add a prefilter to reduce the sediment.
This will make the softening filter last longer and make sure that
some of the buildup is not sediment.
Thank you,
WaterFilters.NET