not too familiar with precision skimmers but if it has just one pump that feeds it water and creates bubbles it is probably an in sump only skimmer, which by your desription is where you have it. in order for it to function properly it MUST have a constant water level. many people have a seperate chamber made for this. depending on your sump size you can just add a baffle to create a constant level compartment for the skimmer.. adding a top off system will help but will not be ideal