Used them for a course filter in outdoor ponds, make sure there's no additive to help dust stick to them, then buy one - cut it up to see if it falls apart - rig up a pump and run water thru it for a month - boil a couple of pieces to see what comes out and what falls apart (it's faster) Then find a good source that won't evaporate in 6-8 months and but 6mo worth. This is why I changes to power floor scrubber pads. And they don't deteriorate either.
Dr Joe
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