the skimmer make bubbles thats how it fills the cup up. if you skimmer is not producin bubbles then you have a problem you need to make an adjustment if you can on that skimmer.
60 ga. SPS tank w/ 2 - 175w 20k halides, korallin 1502 calcium reactor w/ph contorler
24ga. SW nano w/150 HQI
180ga. FW aggresive fish
125ga. FW w/60ga. sump. VERY aggresive fish