I have 2 reef devils and they are great skimmers after a break in period..
I would say you need to get a larger pump... You can try it and see if it works for you it will do no harm to the unit it just won't skim if its not large enough.
You want the water levelt o be at the bottom of the clear riser tube.
I have the pump that came with 1 unit the CA
1800 and i have a viaaqua 2600 on the other. The viaaqua I have cut back some because it was too strong.
Call or email the guys at ETSS if you have any questions. They are a local company for me, I have stopped in at there shop... Nice bunch of guys and real helpful