I beg to differ from Smither's opinion. I've had a Prizm for going on 2 years now and have had very little problems with it. It ran dry once while I was on vacation and I've had to replace the energizer and impeller because of it. Only a $20 fix.
First i cant get the flow right, theres always to much water pouring into the cup
Be sure you have the air intake hose on the correct barb on the collection cup...the left hole is for priming and the right hole is for normal operation.
How long have you had the skimmer? Maybe it just needs a good cleaning, every skimmer will need cleaned out every few months. If its been running in your tank for months, take it out...clean out the intake U-tube, rinse the inside out well and remove the energizer unit from the bottom. The impeller should easily pull out of the energizer and be free of gunk and calcium deposits. Clean out the energizer well and rinse off the impeller. If it looks like there is any calcium build-up then soak the impeller and/or the energizer well with white vinegar. Reassemble and fire it up.
The prizm can be feisty to adjust, prime the unit to get water flowing through and then move the air intake hose to the right hole. Turn back the flow so that it is about a 1/4-1/2" below the rubber "O" ring on the collection cup. You really just have to get a feel for the adjustment, it is touchy but after a month or so I got used to it. If the unit is still overskimming then you may have something in your water that is causing the excessive foam ie. additives or chemicals of some kind. Some coral epoxies will make my skimmer skim like mad for up to a week. All in all, the prizm isn't as nice as some more expensive skimmers, but those of us who bought it probably didn't have the 150-200 for the more expensive skimmers.
Oh ya..if you don't have it, look into getting the filter media basket..great for running carbon and other stuff. HTH