Any skimmer should be producing the same results, that being a dark thick black liquid. If your mix is clear then your skimmer is running too "wet" and the skimmer should be adjusted to remove a "dryer" foam. A wet skimmate will contain desolved organics but it will also remove trace elements to a higher degree than a dry mix.
Chances are that a "wetter" running skimmer would probably yield more mass. But the only way to test would be to evaporate your skim and weigh it dry like back in Chemistry 101.
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