A sea K is right on the money.
I own this skimmer.
I originally set mine up on a new 50 gallon system with a twenty gallon sump. I had very little skim production for the first six months. It would occasionally skim like crazy then go idle for long periods of time.
I finally gave up on it and purchased an Aquamaxx CO-1 skimmer which skimmed consistently from day 1. About a year later the impeller on the Aquamaxx broke and while I was waiting for the replacement I put the Omega back in service and was absolutely shocked by the skim production. It skimmed like crazy, this time for a few weeks and then went idle once again.
I can only conclude the Omega 130 is underrated and should be used on a larger set-up to be more consistent.
From your description, it sounds like your tank is very young, smallish, and probably has very little bio load.
If you want consistent skimming go a different direction. If you stick with the 130, once you have it skimming don't fiddle with it and let it do its thing.
I find that it skims best for me when the outlet is covered in about a 1/4 " of water which I believe is at about 6.5" to 6.75" of water.
Good Luck!