hmm, I have that problem with my coralife skimmer too..
I will unplug the unit, clean out the cup, and plug it back in. It'll make the fine bubles for ahwile, then the bubbles will slow and slow untill no bubbles are seen and the water in the column is clear... I have never been able to figure out what causes this..
90 Gallon Drilled Glass Tank w/ Corner Overflow: 492w (2x 150w 14,000K MH, 2x 96w Actinic CF) Coralife Aqualight Pro | Custom 34x15x15 Sump/Refugium | SWC Skimmer | Coralife Turbo-Twist 6x UV Sterilizer | Maxi-Jet Power Head w/Sure Flow Upgrade Kit | 120lbs of Live Rock | 100lbs of Live Sand