"RichToyBox" wrote in message
news:4lepc.3861$qA.420260@attbi_s51...
Carbon will filter out organic polutants, but is of fixed life span. When
it becomes full, then it can't do anymore. Any carbon filter needs to have
periodic replacement.

Once the carbon in the matting has absorbed all it can, it will actually start
to leach the pllutants back out into the water. You should replace it
regularly, if you use carbon at all. I don't, and have no problems.