vertex in 180 skimmer issues

[Reef Pilot]

Are you sure it is fully closed? If so, there should be zero flow coming out of the outflow pipe, which means that the water has no place to go but up you skimmer column and into the overflow cup.

Is your pump working, ie producing enough flow? And do you have the right pump, with the pinwheel impeller? Is the pump outlet correctly inserted, so that no flow can escape from going into the skimmer?