I give you an example.
I used a XYZ brand small skimmer for a 6ft tank, yes the skimmer skims out kopi-O. Skims out MUD skims out coca cola, pepsi, sarsi etc. So cna I still say it works very well cos it skims out dark stuff?
How do you know it skims your 6 footer clean? NO3, PO4 = 0 ?