How to tell if you're overskimming?

[Vitaminz]

Just my 2 cents worth, because my tank is in an office environment, and because I had overflow of the cup, I just leave the skimmer plugged into the light timmer. So the skimmer only runs for 8 hours of the day, That way I am here in case anything goes wrong. I use to have issues, when it skimmed really good after water changes, or changes to bio load, then do nothing. Just running it 8 hours out of the day, seems to be a nice balance.