Skimmer overflowing + Coral warfare issues ???

[gregzz4]

My skimmer goes berserk now, about a week after a WC
I'm thinking it started doing this after I added a Pulsing Xenia, but I can't be sure
Maybe it's just me ...

1 week after a WC the foam head starts to collapse and I have to dial the skimmer back. Otherwise it will fill the cup rather quickly - as in overnight, or even overflows
The bubbles become small and very 'audible', and the foam is basically 'gone'
I've checked/cleaned the venturi and air inlets - no blockages

Once I do a 10% WC all is good for another week, so it's not related to a blockage
I was thinking it may be related to my sock changes, but the intervals don't jive
It also does not coincide with either carbon or gfo changes

Anyone else notice something similar, or have any input ?