Why wont skimmer build a foam head?

I am at loss at why my Vertex omega 150 will not skim dry or build a foam head at all... It will skim when tuned super wet but then overflow a day later. My bioload is medium in a 100 gallon tank, and I feed mysis, and algae clip for my tang to graze everyday. I run filter socks, and keep the sump clean. The skimmer is in 6.5 inches of water, and has been running for about a month, but the tank has been setup for 8 months. I tried adjusting the nozzle on the pump and the stand pipe. My only thought is maybe I don't have enough flow running through the sump, or not enough? My overflow is a Eshopps 300, with a mag 9.5 tuned down with a gate valve.



Livestock: diamond goby, pair of perc. clowns, blue tang, flame angel, two yellow anthia's, purple fire fish, red firefish. clean up crew is just snails and blue legged hermits