skimmer doing a great job of skimming out dark and disgusting doc from ur tank does not mean that ur tank parameters r in good conditions.
let me put it this way,
wld u rather hv ur skimmer skimming out lots of gunk everyday but u still get high nutrients (NO3, PO4, etc) readings?
or wld u rather ur skimmer skims out little gunk but u get ur ideal water parameters condition?
hope u get what i m trying to say.