skimmer help please!

[ctenopoma]

I just bought a used red sea "prizm pro deluxe" does anyone own this model?
it's producing foam but I'm not sure if it's set up right. I have it hanging on the back of my tank. I have to turn the input water valve almost completely closed to get it to start foaming. if I turn the flow up microbubbles start being released into the tank from the output and the foaming stops. It could just be that my tank hasn't had a skimmer on it for awhile but I thought because it's used there wouldn't be a "break-in" period.

if anyone could offer any advice I would greatly appreciate it!

I'll try to add pics tomorrow to show whats going on.