If it ain't working right, you don't have it set up right. I have one on a 55 reef and it works great. Just a few things.
1. the air hose MUST be plugged into the right nipple on the collection cup. Read your instructions.
2. Make sure the cover on the collection cup is pushed on tight, this keeps it from ever overflowing.
3. Fill the chamber with the intake tube with water. This quiets the unit.
4. Keep the top of the collection cup off. Set the water adjustment so that you just see popping bubbles every so often in the throat of the unit. Be patient and wait until it settles into a rythm. Then replace the cover and let it alone.
5. When the collection cup fills, UNPLUG THE UNIT, and clean the cup. Replace the cup and plug the unit back in. This keeps you from having to readjust the setting. I have not touched my setting in about 4 months. It fills at a very constant rate, I dump it about every 3rd day, and it is a dark green syrupy skimate. My tank looks crystal clear.
6. If you want to get fancy, go buy one of those 10 dollar surface skimmer attachments for an aquaclear or Eheim filter. Remove the bottom cone on the prizm and tape the end of the skimmer hose with electrical tape. Set up the skimmer to only skim from the top. I set mine up this way, and it totally eliminates the surface crud.
Hope this helps.
Ed