PM skimmer

[PrairieReefer]

I have never looked at a PM skimmer, but there should be an air valve of some type on the airline attached to your venturi. Reduce the airflow until you are producing a nice dry foam in the neck of the unit, without foaming into and filling the cup. The dry foam will slowly build up and push into the cup without emptying your sump. You will have to do some playing around with the setting for a few days, until the unit is broke in (even if used, after being cleaned etc, the skimmer will foam differently until there is a little film on the plastic). Also certain additives can cause unexpected foaming for a few hours, so keep an eye on it when you put anything into the aquarium water, until you know which will cause problems.

BTW Excess airflow causes the foaming, excess water flow pushes fine bubbles into your sump

Hope that was some help.